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.¹ 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,² and babies born to mothers who smoke have more than twice the risk of dying from sudden baby death syndrome (SIDS).³

Weight Gain in Pregnancy

No single maternal weight gain target meets the needs of all women. The amount of weight a woman optimally gains varies with her height, age, plans to breast feed, and whether she is delivering twins. However, a few basic guidelines are generally accepted:⁴ Women who enter pregnancy at more than 120% of standard weight still have an obligatory weight gain of 15–25 pounds at a rate of about 0.7 pounds per week. Women who are at ideal body weight and are not going to nurse have a target of gaining about 22 pounds overall at a rate of 0.8 pounds per week. Women who enter pregnancy between 90% and 110% of ideal body weight and plan to nurse have a target weight gain of 25–35 pounds overall at a rate of 0.9 pounds per week during the second and third trimesters. Physically immature adolescents and women less than 90% of ideal body weight have a target weight gain of 32 (28–40) pounds at a rate of 1.1 pounds per week. Women who know they are going to have twins have a target weight gain of 40 (35–45) pounds with a weekly rate of 1.4 pounds during the last 20 weeks of pregnancy.

Another way to determine the appropriate weight gain for pregnancy is by using the Body Mass Index (BMI). The BMI is calculated by dividing your body weight (in kilograms) by the square of your height (in meters). (A kilogram is equal to 2.2 pounds; a meter is equal to about 39 inches.) According to the standard set in 1990 by the Institute of Medicine (IOM) of the National Academy of Sciences,⁵ a woman with a low BMI (less than 19.8) should gain a total of 12.5–18 kg (27.5–39.7 pounds) during pregnancy; a woman with a normal BMI (19.8–26) should gain a total of 11.5–16 kg (25.4–35.3 pounds) during pregnancy; a woman with a high BMI (greater than 26.0–29.0) should gain a total of 7–11.5 kg (15.4–25.4 pounds) during pregnancy. Adolescents and black women should strive for gains at the upper end of the recommended range. Short women (less than five feet) should strive for gains at the lower end of this range. Obese women (BMI greater than 29) have a separate recommended target weight gain of about 6 kg (13.2 pounds). Published studies suggest that only 30–40% of American women actually have weight gains within the IOM’s recommended ranges.^{6, 7, 8}

Although the IOM’s national recommendations concerning pregnancy weight gain have been widely adopted, they have not been universally accepted.⁹ The amount of weight gain during pregnancy varies considerably among women with good pregnancy outcomes.^{10, 11} For that reason, weight gain alone is not likely to be a perfect screening tool for pregnancy complications. Nevertheless, weight gains outside the IOM’s recommended ranges are associated with twice as many poor pregnancy outcomes than are weight gains within the ranges. A systematic review of all studies published between 1990 and 1997 that specifically examined foetal and maternal outcomes showed that weight gain within the IOM’s recommended ranges is associated with the best outcome for both mothers and infants.¹²

Weight loss programmes are not generally recommended during pregnancy. Nevertheless, it should be noted that being overweight while pregnant increases the incidence of various conditions in both the mother and the foetus, such as gestational diabetes and blood pressure problems. The risk is proportional to the amount of excess weight. Overweight women have a higher risk of caesarean deliveries and a higher incidence of anaesthetic and post-operative complications in these deliveries. Poor responsiveness in the newborn, large head, and some birth defects are more frequent in infants of obese mothers. Maternal obesity increases the risk of newborn death. The average cost of hospital prenatal and postnatal care is higher for overweight mothers than for normal-weight mothers. Infants of overweight mothers require admission into intensive care units more often than do infants of normal-weight mothers.¹³

Some women will be concerned that the IOM’s recommended weight gain will result in too much weight gain or more weight retention after the baby is born, but there is no evidence to support this concern. Although there are risks associated with being overweight during pregnancy, dieting during pregnancy can seriously endanger the health of the foetus. A low rate of pregnancy weight gain has been shown, in most studies, to increase the risk of premature delivery.¹⁴ There is no evidence that restricting normal weight gain in pregnancy is either safe or beneficial.¹⁵