Reproduction in Mammals

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Reproductive System

I

INTRODUCTION

Reproductive System, term applied to the group of plant or animal organs that are necessary for or that are accessory to the reproductive processes (see Reproduction). The basic units of sexual reproduction are the male and female germ cells; this article deals with the organs within which the germ cells of animals mature and are stored, the organs through which they are transported in the process of producing a new individual, and accessory glandular organs. For the reproductive organs of plants, see Plant Propagation.

II

ORIGIN OF THE REPRODUCTIVE CELLS

When the embryo of any sexually reproducing animal is undergoing cell division, certain cells, known as primordial germ cells, which are produced by such division, remain in an undifferentiated state. Cells other than primordial germ cells are known as vegetative cells or somatic cells; these cells become differentiated into tissues and organs. In invertebrates, the primordial germ cells congregate in the body cavity or in a section of the circulatory system; in vertebrates, these cells are located in organs that adjoin the excretory system. The tissues in which the germ cells lodge become reproductive organs known as gonads. These organs are embryologically derived from primitive kidneys located in the anterior, lateral part of the body; in most mammals, they shift before birth to the posterior, ventral region of the body. The primordial germ cells remain inactive in the gonads until the animal reaches sexual maturity, when the undifferentiated cells undergo a great number of normal cell divisions or mitoses. In the process of developing into mature reproductive cells or gametes, the germ cells undergo a special type of cell division, known as meiosis, which halves the number of chromosomes they carry. At the time of sexual maturity, the somatic cells composing the gonads of higher animals begin to secrete hormones that control the appearance of the various secondary sexual characteristics (see Sex).

III

GONADS

Organs that contain germ cells which later develop into male gametes or spermatozoa are known as testes or male gonads. Organs that contain germ cells which later develop into female gametes, eggs, or ova are known as ovaries. In many invertebrate species individual animals bear both testes and ovaries (see Hermaphroditism). In some invertebrates, and in most vertebrates, individuals bear either testes or ovaries, but not both sets of organs. In invertebrates, a single animal may have as many as 26 pairs of gonads; in vertebrates, the usual number is 2. Cyclostomes and most birds are unusual among vertebrates in possessing only a single gonad; owls, pigeons, hawks, and parrots are unusual among birds in having two gonads. The size of gonads increases at sexual maturity because of the great number of germ cells produced at that time; many germ cells are also produced during breeding seasons so that many animals have a seasonal increase in size of the gonads. During the breeding season of fish, the ovaries increase in size until they constitute about one-quarter to one-third of the total body weight.

The testes and ovaries of mature animals differ greatly in structure. The testes are composed of delicate convoluted tubules, known as seminiferous tubules, in which the primitive germ cells mature into spermatozoa. The testes of mammals are generally oval bodies, enclosed by a capsule of tough connective tissue. Projections from this tough capsule into the testis divide the testis into several compartments, each of which is filled with hundreds of seminiferous tubules. The mature spermatozoa are discharged through a number of ducts, called the efferent ducts, which communicate with the epididymis, a thick-walled, coiled duct in which the sperm are stored.

In all vertebrates below marsupials on the zoological scale, and in elephants, sea cows, and whales, the testis remains within the body cavity during the lifetime of the animals. In many mammals, such as rodents, bats, and members of the camel family, the testis remains within the body cavity during periods of quiescence, but moves into an external pocket of skin and muscle, known as the scrotum, during the breeding season. In marsupials, and in most higher mammals, including the human male, the testes are always enclosed in an external scrotum. During fetal life, the testes move through the muscles composing the posterior, ventral portion of the trunk and carry with them the portion of the peritoneum and skin surrounding these muscles. The channel in the muscles through which the testis moves is known as the inguinal canal; it usually closes after birth, but sometimes remains open and is then often the site of herniation (see Hernia). The portion of the peritoneum that the testis carries with it forms a double wall of membrane between the scrotum and testis and is known as the tunica vaginalis. Occasionally, the testes in the human male do not descend into the scrotal sac; this condition of nondescent, which is known as cryptorchidism, may result in sterility if not corrected by surgery or the administration of hormones. Retention of the testes within the body cavity subjects the germ cells to temperatures that are too high for their normal development; the descent of the testes into the scrotum in higher animals keeps the testes at optimum temperatures.

Unlike germ cells in the testis, female germ cells originate as single cells in the embryonic tissue that later develops into an ovary. At maturity, after the production of ova from the female germ cells, groups of ovary cells surrounding each ovum develop into “follicle cells” that secrete nutriment for the contained egg. As the ovum is prepared for release during the breeding season, the tissue surrounding the ovum hollows out and becomes filled with fluid and at the same time moves to the surface of the ovary; this mass of tissue, fluid, and ovum is known as a Graafian follicle. The ovary of the adult is merely a mass of glandular and connective tissue containing numerous Graafian follicles at various stages of maturity. When the Graafian follicle is completely mature, it bursts through the surface of the ovary, releasing the ovum, which is then ready for fertilization; the release of the ovum from the ovary is known as ovulation. The space formerly occupied by the Graafian follicle is filled by a blood clot known as the corpus hemorrhagicum; in four or five days this clot is replaced by a mass of yellow cells known as the corpus luteum, which secretes hormones playing an important part in preparation of the uterus for the reception of a fertilized ovum. If the ovum goes unfertilized, the corpus luteum is eventually replaced by scar tissue known as the corpus albicans. The ovary is located in the body cavity, attached to the peritoneum that lines this cavity.

The functioning of both male and female gonads is under the hormonal influence of the pituitary gland.

Ovum and Sperm

IV

TRANSPORTATION OF THE REPRODUCTIVE CELLS

Before being discharged from the body, the reproductive cells travel from the gonads to an external body opening. In many invertebrates, and in a few aquatic vertebrates, the reproductive cells are discharged into water directly from the gonads through pores in the body wall. In higher animals ducts carry the reproductive cells into the urinary or cloacal excretory systems, or into independent reproductive passages.

In male vertebrates, the ducts are directly connected to the testes. The male ducts include the epididymis, which lies attached to the testis, and which transports the male gametes to the vas deferens. The vas deferens carries the spermatozoa to the ejaculatory duct, the contractions of which cause the discharge of sperm into the posterior urethra.

In most fishes, the ovary has a hollow expansion through which the ova pass into the cloaca. In most other vertebrates, however, no direct connection exists between the ovary and the oviducts that carry the ova into the cloaca or into the independent external opening. In mammals, when the Graafian follicle bursts, the egg falls toward the interior of the abdominal cavity. The oviduct (known in higher mammals as the fallopian tube) has an open, funnel-shaped end located near the ovary, and the mature egg is drawn into the funnel by ciliary action. Occasionally, the egg misses the open end of the oviduct and falls into the abdominal cavity; such eggs are capable of being fertilized, resulting in ectopic pregnancies (see Pregnancy and Childbirth). In animals lower than marsupials the oviducts open directly into the cloaca; in marsupials and placental mammals, the oviducts, two of which are normally present, fuse at their cloacal ends to form a thick, muscular organ, the uterus or womb, in which the young develop, and a thinner channel, the vagina, which opens exteriorly.

sperm, ova

V

GENITALS

In animals that lay their eggs and discharge their sperm into water, the spermatozoa reach the eggs by chemical attraction; the eggs of individuals of a species attract only the sperm of members of the same species. When eggs and sperm are deposited at great distances from each other, the number of eggs fertilized is small. Many amphibians and aquatic vertebrates solve this problem by attaching themselves to their mates by means of holdfast mechanisms, such as claspers; when the female of these animals deposits the eggs, the male can immediately deposit sperm in the same location.

In terrestrial animals, various adaptations have been developed whereby internal fertilization of the eggs may be produced. The male snake, which discharges the spermatozoa through a cloaca, has, for example, anal hooks that are inserted into the cloaca of the female during the breeding season. These hooks bind the male and the female together while the spermatozoa are being discharged. External reproductive organs used by animals to facilitate internal fertilization are known as genitals or genitalia.

The male genital of all mammals above the monotremes is the penis, a protrusible, erectile organ that directs the spermatozoa into the female cloaca or vagina. In turtles and crocodiles, which are the most primitive animals possessing the organ, the penis is located on the ventral wall of the cloaca and is grooved along its upper side. The spermatozoa travel along the groove into the female cloaca. In marsupials and placental mammals, the penis is a closed tube, composed of three bundles of tissue, bound together by connective tissue and covered with loose skin. Two large bundles of tissue, known as the corpora cavernosa, constitute the upper portion of the penis; these bundles contain numerous compartments that are filled with blood during sexual excitement, causing the penis to become stiff and erect. The flow of blood into the corpora cavernosa is controlled by sacral spinal nerves. Below and between the corpora cavernosa is the third bundle of tissue, which is known as the corpus spongiosum; this bundle is perforated by the urethra and, in several lower mammals, also contains a bone that serves to further stiffen the male genital. At the terminal end of the penis is a sensitive cap known as the glans; in marsupials the glans is forked. In many mammals, the male genital, when not erect, is withdrawn into a sheath in the body. In primates, including the human male, the penis is pendant, and the glans is covered with a layer of retractile skin, known as the prepuce or foreskin, which corresponds to the sheath of lower animals.

The chief female genital is known as the vagina. This organ is present in all marsupials and placental mammals. In marsupials, two vaginas and two uteri are present; in primates, including the human female, only one vagina is present; and in mammals intermediate in development between the marsupials and primates, various degrees of partially united, double vaginas are present. The external end of the vagina is covered in virgin primates by a membrane, known as the hymen. Anterior to the hymen is the external opening of the urethra. The urethra and the opening of the vagina are contained in an indented space which is known as the vestibule. In primates, two membranous folds, known as the labia minora, are found on either side of the vestibule. In primates, including the human female, two additional folds, the labia majora, enclose the labia minora. The clitoris, at the front of the labia, is homologous with the penis although greatly reduced in size (see Homology below).

VI

ACCESSORY GLANDS

Among the glands accessory to the reproductive process are those that provide a fluid medium in which the spermatozoa may live, those that produce mucus which reduces friction during copulation, those that emit alluring odors to members of the opposite sex, and those that secrete nourishment for the ova, the embryos, and the newborn young.

The seminal vesicles of the male have already been mentioned as organs that secrete mucus. The most important male accessory gland is the prostate gland, a compound gland about the size of a chestnut located at the base of the urethra where the urethra leaves the bladder and enters the penis. The prostate secretes a thin milky fluid with a characteristic odor; this fluid constitutes the greater part of the semen that is deposited in the female vagina and that contains the spermatozoa. The prostate gland is present only in placental mammals, and among these mammals is absent in edentates, martens, otters, and badgers. Cowper's glands are two small glands, about the size of a pea, located on each side of the base of the penis. Their secretion is thick and clear and is believed to protect the spermatozoa against excess vaginal acidity. Cowper's glands are absent in bears, dogs, and aquatic mammals.

The primary lubricating glands of the female are the cervical glands, located in the uterus where the uterus communicates with the vagina, and Bartholin's glands, located in the vestibule between the hymen and the labia minora. Both sets of glands secrete mucus. Female placental mammals also have uterine glands that prepare the uterus for the reception of the fertilized egg.

The anal glands of many mammals secrete special substances called pheromones, which signal reproductive readiness by scent to members of the opposite sex. Pheromones may occur in other glandular secretions as well.

Among the different structures serving to nourish the young, the placenta of placental mammals is unique (see Fetus). The mammary glands of mammals are also included among accessory reproductive glands (see Breast). Female egg-laying animals have albumen glands, which coat the zygote with nutrient albumen before the egg is laid, and nidamental glands, which surround the zygote and albumen with a leathery or calcareous shell.

VII

HOMOLOGY

The sex of a young embryo is indistinguishable, males and females passing through similar embryonic stages. Embryo males and females develop almost a duplicate set of reproductive organs, one set becoming vestigal shortly before birth, and the other set becoming prominent. Most cases of so-called mammalian hermaphroditism are actually cases of abnormal development in which external genitalia similar to those of both sexes have been developed. For example, mammalian females have a small, erectile organ, consisting of two corpora cavernosa, located in the upper portion of the vestibule. This organ, called the clitoris, is homologous with the male penis; except in lemurs and a few rodents it does not contain the urethra, which is usually located beneath the clitoris. In species in which the male possesses a penis bone, the clitoris of the female contains a small bone.

Contributed By:
Jean Roche

Menstrual Cycle

Menstruation
An average menstrual cycle begins with three to five days of menstruation, the shedding of the uterine lining, during which hormone levels are low. At the end of menstruation, a pituitary hormone stimulates new follicles to develop in the ovary. These secrete estrogen as they mature, causing cells in the lining of the uterus to proliferate. Mid-cycle, one mature follicle releases an egg. The empty follicle forms the corpus luteum, an endocrine body that secretes progesterone. Under the added influence of progesterone, the uterine lining thickens further and swells in preparation for the implantation of a fertilized egg. If fertilization does not take place, the corpus luteum dies and hormone levels fall. Without hormonal support, the uterine lining disintegrates and discharges, beginning a new menstrual period and cycle.

Menstruation, periodic vaginal discharge in humans and other mammals, consisting of blood and cells shed from the endometrium, or lining of the uterus (see Reproductive System). Menstruation accompanies a woman's childbearing years, usually beginning between the ages of 10 and 16, at puberty, and most often ceasing between the ages of 45 and 50, at menopause. Menstruation is part of the process that prepares a woman for pregnancy. Each month the lining of the uterus thickens; if pregnancy does not occur, this lining breaks down and is discharged through the vagina. The three to seven days that menstruation lasts is called the menstrual period.

In most women the menstrual cycle is about 28 days, but it can vary considerably even from one month to another. The cycle is initiated by hormones in the blood that stimulate the ovaries (the two female organs that produce ova, or eggs). Each month, hormones cause an egg in one of the two ovaries to mature (to become capable of being fertilized and develop into a fetus). The ovaries also produce hormones of their own, primarily estrogen, which cause the endometrium to thicken. About midway through the menstrual cycle, 14 to 15 days before the next period, the ovary releases the mature egg in a process called ovulation. The egg passes through the fallopian tube to the uterus. If the egg unites with a sperm on its way to the uterus, fertilization occurs and pregnancy ensues.

The three to five days the egg takes to reach the uterus after being released by the ovary is known as the woman's fertile period. If fertilization does occur, the fertilized egg attaches itself to the enriched uterine lining and pregnancy continues. Menstruation does not occur during pregnancy, and a missed period is often the first indication of pregnancy a woman notices (see Pregnancy and Childbirth). If fertilization does not occur, the lining of the uterus does not receive the hormones it needs to continue the thickening process. Thus, the uterine lining breaks down and is discharged from the body during menstruation.

Many women experience premenstrual discomfort. Tenderness of the breasts and a tendency to retain fluid (bloat) are common one to seven days before each period. Some women also experience a condition called premenstrual syndrome (PMS), which is characterized by headaches, irritability, nervousness, fatigue, crying spells, and depression with no apparent cause. A few women also experience menstrual cramps (dysmenorrhea) during the first day or two of the period. Although premenstrual symptoms and discomfort during menstruation were once thought to be of psychological origin, research now indicates that hormonal and chemical changes are responsible. New medications are effective in treating these problems.

Contributed By:
Michaela P. Richardson

Human Embryo Development

A new human being progresses from a single cell to an embryo, and from an embryo to a fetus during the first eight weeks of development. In this brief time, the developing human changes dramatically from one cell to a recognizable human form in which the rudimentary nervous, digestive, respiratory, and other body systems have been established.

DAY ONE The first cell of a new human being, called a zygote, is formed when a sperm fertilizes an egg. In the egg cell shown here, the nuclei of the sperm and egg appear as two yellow-brown, irregular shapes. When these two nuclei fuse, fertilization is accomplished.

DAY THREE The zygote begins its journey down the Fallopian tube. About 36 hours after fertilization, cell division begins in the Fallopian tube, and continues to occur about twice a day. In three to four days, the cluster of dividing cells completes the 10 cm (4 in) journey through the Fallopian tube to the uterus.

DAY SIX About the fifth day after fertilization, a cluster of about a hundred cells floats in the uterus. It soon takes the form of a fluid-filled ball of cells called a blastocyst. After one or two days in the uterus, the blastocyst burrows into the uterine lining, which grows over the blastocyst and provides it with nutrients. This process is known as implantation, and the blastocyst is now called an embryo.

DAY TWENTY EIGHT After implantation, cells of the embryo begin to specialize and form primitive organs. In the four week-old embryo shown here, the head (bottom, left) can be distinguished. The heart beats, and limb buds of the arms and legs are visible. The placenta develops at this stage and provides the embryo with nutrients from the mother. The four-week-old embryo measures about 5 mm (about 0 .2 in) from crown to rump.

DAY FIFTY SIX After eight weeks of development, all the rudimentary structures of a human have formed, and the embryo passes into the fetal stage of development. The fetus shown here floats in the watery amniotic fluid, which is contained by the transparent, tough, amniotic membrane. The amniotic fluid acts as a shock absorber, preventing damage to the developing fetus. The eight-week-old fetus measures about 30 mm (about 1.2 in) from crown to rump.

Placenta & Umbilical Cord

Placenta and Umbilical Cord

Placenta

The placenta is responsible for respiration and excretion in the growing fetus. Fetal blood flows through the blood vessels of the umbilical cord to the placenta, where fingerlike capillary nets are surrounded by pools of the mother’s blood. Here carbon dioxide and other metabolic wastes diffuse from fetus to mother, and oxygen and nutrients pass from mother to fetus. Some STDs can be passed from an infected mother to her unborn child when disease-causing organisms cross the placenta.

Umbilical Cord, long flexible cord that allows a fetus to be nourished as it grows and develops within the uterus, or womb. On one end, the cord attaches to the abdominal area of the fetus. On the other end, the cord attaches to the placenta. It is in the placenta that the blood vessels of the mother and fetus exchange contents from each other’s circulatory systems. The umbilical cord contains two large arteries, which deliver oxygen and nutrients to the fetus from the placenta, and one large vein, which carries carbon dioxide and other wastes from the fetus to the placenta. Transferred to the bloodstream, most of these wastes are soon eliminated through the mother’s excretory system.

As the fetus approaches birth, the umbilical cord is about 50 cm (20 in) long and has a diameter of 1.5 cm (0.5 in). Shortly after delivery, the cord is clamped in two places and severed between the clamps. The infant is thereby separated from the placenta, with the clamps preventing unnecessary loss of blood. The small portion of the cord left attached to the baby’s abdomen withers, and within a week or ten days it falls off the infant’s body. The resulting scar is known as the umbilicus, navel, or belly button.

Breast Milk Compare with bottled milk

Human milk provides distinct advantages over formula or cow milk for human infants. Not only is breast milk’s nutritional composition uniquely designed for the needs of human babies, but it also contains antibodies from the mother’s immune system that help the infant fight off infections and diseases. During the first few days after giving birth, a mother releases colostrum, a yellowish liquid that contains less fat and lactose and more protein and antibodies than regular breast milk. After about three or four days, colostrum is replaced by a bluish-white milk that is higher in fats and carbohydrates, reflecting the energy needs of a growing baby (see Breast-feeding).

Questions and Answers regarding Dietary needs of a Pregnant woman

Q: I consumed some alcohol before I knew I was pregnant. Should I take any special precautions or have any extra tests?

A: This is not an unusual situation. Because we know alcohol enters the unborn baby’s circulation, many pregnant women worry that they may have caused harm to the baby because they drank before realizing they were pregnant. Effects of alcohol are dose-related to some extent. If you drank very heavily and often before you discovered you were pregnant, the effects on the baby are potentially greater than if you drank too much on one occasion or drank lightly on several occasions.

There are no extra tests during pregnancy that can tell you if your baby is affected. The usual observations made by your doctor or midwife (such as height measurements, heart rate monitoring, and possibly ultrasound) can detect some problems, such as growth retardation, that are sometimes associated with alcohol use. Observations of the baby after birth will allow a clearer assessment of the baby’s condition.

The two best things for you to do during pregnancy are to stop drinking alcohol (because the baby receives alcohol in his or her bloodstream whenever you drink) and to try not to worry (which, I realize, is easier said than done). Babies are resilient and not all babies whose mothers drank have apparent alcohol-related problems. Discuss your concerns with your doctor, and maintain a healthy lifestyle.

Q: Is it true that I should not clean my cat’s litter box while I am pregnant? Why?

A: Kitty litter carries the potential for spreading toxoplasmosis, a mild infection that may cause coldlike symptoms under normal circumstances. If you are pregnant, however, toxoplasmosis can cause serious malformations or even death of the unborn baby.

Cats, especially outdoor cats that eat rats or mice, often carry the organism that causes toxoplasmosis. You can get toxoplasmosis by petting a “carrier cat,” changing its litter box, or gardening in soil where cats have passed feces. You can also get toxoplasmosis from eating raw or undercooked meat and eating unwashed vegetables that have grown underground, such as potatoes or carrots.

It is quite likely that if you have had an outdoor cat in the past, you have had toxoplasmosis. Once you have had the disease, you are immune to it in the future. The problem is that most people do not know whether they have had it or not. If you have a cat and are concerned, you can be tested for antibodies to toxoplasmosis (which indicate that you have had the disease and are now immune to it). An absence of antibodies indicates that you are at risk. To prevent catching toxoplasmosis during pregnancy, take the following precautions:

* Cook your meat thoroughly.

* Wash your vegetables thoroughly.

* Wash your hands after you pet or handle a cat.

* Have someone else clean the litter box.

* Avoid soil and sandboxes where cats pass feces.

Q: What are the benefits of folic acid for pregnant women?

A: Folic acid supplements should be taken a month or more before conception and continued through early pregnancy. Most prenatal vitamin supplements contain the recommended daily amount of folic acid (400 micrograms).

The main benefits of folic acid are the prevention of particular birth defects, such as cleft lip, cleft palate, and neural tube defects (abnormalities in the development of the brain and spinal cord, such as spina bifida and anencephaly, the absence of a large portion of the brain). These defects occur in about 1 in 1,000 newborns but are dramatically reduced when women take folic acid before and during early pregnancy.

Folic acid is present in foods such as liver, leafy green vegetables, and yeast. It is difficult for many women to get enough folic acid through their diets. For this reason folic acid is added to prenatal vitamin preparations.

Because women with unplanned pregnancies might not get enough folic acid before pregnancy, nutritionists and maternity caregivers recommend that all fertile women take a folic acid supplement every day, whether planning pregnancy or not.

Q: Is it safe for me to get a massage during pregnancy?

A: Yes, it is safe and very helpful as well. You should, however, see a licensed massage therapist (LMT) who has had additional training in pregnancy massage. She or he will know how to safely modify massage techniques to accommodate for bodily changes that occur during pregnancy (for example, avoiding having you lie on your back or your abdomen after about four to five months of pregnancy and checking for varicose veins, excessive swelling, carpal tunnel syndrome, and other conditions).

Many massage therapists have specially designed massage tables that allow you to lie on your abdomen without putting undue pressure on your abdomen or breasts. Ask your doctor, midwife, childbirth educator, or doula for referrals.

Q: Do midwives assist only with home births?

A: No, most midwives practice in hospitals or out-of-hospital birth centers because those are the locations where most women give birth. It is true, however, that almost all home births are attended by midwives, who are experts in normal birth.

In all countries outside North and South America, midwives provide most of the maternity care, but in the United States less than 10 percent of all births are attended by midwives. The percentage is growing rapidly, however, because midwifery care is highly satisfying to women and has an excellent track record in terms of safety and cost.

Q: I was wondering when a woman can get pregnant. What are the days in the menstrual cycle that you are most likely to get pregnant? How do you determine when you are fertile in your own menstrual cycle?

A: There are only a few days before and after you ovulate when you are able to become pregnant. These days come roughly in midcycle, but timing of ovulation varies from woman to woman. There are several ways that you can determine when you ovulate, including observing changes in the mucus in your vagina (cervical mucus) and recording your temperature before rising each morning.

An excellent book on the subject is Taking Charge of Your Fertility, by Toni Weschler (HarperPerennial, 2001). It provides complete and very helpful information on this subject and many others.

Q: What effects does stress have on pregnancy and what are the symptoms?

A: Stress during pregnancy may be related to a woman's relationship to family and friends. Major life-changes, such as a death in the family, change in marital status, serious illness, or moving also play a significant role in stress levels. Financial situation and job or career demands are other common sources of stress.

Whatever its cause, stress can manifest itself as anxiety, exhaustion, fear, sadness, anger, or grief. Such emotions can lead to physiological changes, such as increased release of stress hormones and increased blood pressure. These effects of stress may cause premature labor or hypertension (high blood pressure). Both conditions can present problems for the baby, such as causing the baby to be small in size or immature in development.

Pregnancy adds stress to the lives of women who are already stressed. The right caregiver (midwife, doctor, or clinic) may be able to refer such women to appropriate services that can ease some of their stress.

Stress management techniques are also helpful. Many women find that yoga, meditation, and relaxation techniques help reduce stress. Self-help methods or counseling can help a woman learn how to avoid, eliminate, or better respond to stressful circumstances. The most important thing is practical and emotional support from loved ones and friends.

One important note: A pregnant woman in stressful circumstances must be careful not to blame her baby. Doing so may lead to inappropriate treatment of her innocent baby. Rather, she should address the real causes of her stress and reserve love and concern for her baby.

Q: Is it okay for me to eat sushi with raw fish while I am pregnant?

A: You should not eat sushi with raw fish because it sometimes contains parasites such as tapeworms. These parasites can make anyone sick, whether pregnant or not. The added risk during pregnancy is that your unborn baby could be deprived of necessary nutrients if your illness lasts for a long time.

When you are pregnant, cook fish well so as to kill any parasites, rather than follow the current trend of lightly searing the fish. Cook fish until it flakes when you insert a fork and twist it. Follow preparation directions in a good cookbook to determine cooking times for various kinds of shellfish. Freezing fresh seafood also kills parasites.

Today another concern regarding seafood is industrial pollution, which contaminates seafood in some geographical areas with chemicals or PCBs (polychlorinated biphenyls). Cooking does not destroy these substances. You should check with your community health department for information on the safety of local seafood.

Q: What vitamin supplements should I take during pregnancy?

A: Your best source of vitamins is nutritious food from all the food groups: grains; vegetables; fruits; calcium foods such as dairy products; protein foods such as meat, fish, poultry, eggs, dried beans, and nuts; and fats, oils, and sweets. Most doctors and midwives recommend a good diet plus prenatal vitamins for extra insurance. Prenatal vitamins are preferable to ordinary multipurpose vitamins because they are designed to meet the added nutritional demands of pregnancy.

It is also important to have your diet evaluated by a nutritionist. If you lack certain nutrients due to food allergies, intolerance, or dislike, additional amounts of specific supplements (such as calcium, iron, and others) may be recommended. A nutritionist can help you plan a diet that is in line with your taste preferences and consistent with your ethnic or religious background.

As for the decision on the specific choice of the brand and formula for your prenatal vitamins, there are numerous ones available. You and your doctor or midwife should make the choice jointly.

It is not wise or safe to take large doses of any vitamins, or to design your own supplementation program, without professional guidance. Vitamins have potential side effects on your unborn baby. One example is vitamin C, which, if taken in large quantities over several weeks or months (in hopes of preventing colds), creates a higher than usual requirement in the unborn baby, which continues after birth, causing temporary symptoms of vitamin C deficiency. Vitamins should be considered a form of medicine and taken with caution and knowledge.

Q: About how much weight should I gain during pregnancy?

A: If you are of normal weight before pregnancy, you should probably gain between 20 and 35 pounds. This weight gain includes the growing baby, as well as many of the changes your body undergoes to support the baby. The breakdown typically looks something like this:

Baby 6 to 9 pounds

Placenta 1 to 2 pounds

Uterus 2 pounds

Amniotic fluid 2 to 3 pounds

Added breast weight 1 to 2 pounds

Added blood volume 2 to 3 pounds

Added tissue fluid 4 to 6 pounds

Fat 5 to 8 pounds

Total weight gain 23 to 35 pounds

If you were underweight or overweight before pregnancy, you may benefit from gaining more or less than the recommendations for women of normal weight. Ultimately, the quality of your diet is more important than the number of pounds you gain during pregnancy.

Q: What is a doula, and why do women use doulas for assistance during childbirth?

A: A doula is a woman (or occasionally a man) who is trained and experienced in helping with childbirth. She accompanies women and their partners through the entire birth process, providing emotional support, physical comfort, and nonclinical advice. She also helps them get the information they need to make good decisions.

Women and their partners choose doulas for a number of reasons:

* The doula puts the parents’ interests first.

* The doula is knowledgeable and caring.

* The doula can help parents have the kind of birth they want and make adjustments if problems arise and unexpected interventions are needed for safety.

* The doula does not leave for a break or shift change. (Doulas take breaks only when the woman is asleep or when labor is unusually long and a backup doula is present.)

* Women who are anxious or fearful about birth or hospitals appreciate the support and reassurance a doula gives.

* Partners often feel overwhelmed by their responsibilities and want help and advice in carrying out their roles. They also appreciate being able to take a nap during a long labor without leaving the mother with no support.

* Expectant parents are impressed by research findings from numerous studies that prove that a doula’s support often results in shorter labors, fewer requests for epidural blocks, fewer cesarean births, fewer deliveries by forceps and vacuum extractor, and less postpartum depression.