Pregnancy, the period during which a woman’s fertilized egg (embryo) gestates and becomes a fetus, lasts an average of 40 weeks from the date of the last menstrual period to delivery of the infant.

In the first trimester (13 weeks), many pregnant women experience nausea. Usually these women report that they feel best during the second trimester. During the third (final) trimester, the increasing size of the fetus begins to place mechanical strains on the expectant mother, often causing back pain, leg swelling, and other health problems.

Dietary changes that may be helpful

Nearly all pregnant women can benefit from good nutritional habits prior to and during pregnancy. The increased number of birth defects during times of famine attest to the adverse effects of poor nutrition during pregnancy. For example, in a dietary survey of pregnant women, higher dietary intake of niacin (a form of vitamin B3) during the first trimester was correlated with higher birth weights, longer length, and larger head circumference (all signs of healthier infants).

Women who consume a standard Western diet (high in fat and sugar and low in complex carbohydrates) during pregnancy and breast-feeding may not be obtaining adequate amounts of essential vitamins and minerals; this can result in health problems for the newborn. Pregnant women should choose a well-balanced and varied diet that includes fresh fruits and vegetables, whole grains, legumes, and fish. Refined sugars, white flour, fried foods, processed foods, and chemical additives should be avoided.

Consumption of moderate to large amounts of caffeine while pregnant has been associated with an increased risk of miscarriage. Although some studies suggest that only very large amounts of caffeine increase the risk of miscarriage, an analysis of clinical trials found that women who consumed more than 150 mg of caffeine (roughly one to two cups of coffee) per day while pregnant had an increased risk of miscarriage or delivering a baby with a low birth weight. The FDA has advised women to avoid drinking coffee and consuming other caffeine-containing foods and beverages during pregnancy.

Lifestyle changes

A woman can reduce her risk of complications during pregnancy and delivery by avoiding harmful substances, such as alcohol, caffeine, nicotine, recreational drugs, and some prescription or over-the-counter drugs.

Even minimal alcohol consumption during pregnancy can increase the risk of hyperactivity, short attention span, and emotional problems in the child. Pregnant women should, therefore, avoid alcohol completely.

Cigarette smoking during pregnancy causes lower birth weights and smaller-sized newborns. The rate of miscarriage in smokers is twice as high as that in nonsmokers, and babies born to mothers who smoke have more than twice the risk of dying from sudden infant death syndrome (SIDS).