Pregnancy Term & Due Date

Pregnancy refers to the condition of a woman over a period of time (~9 months) during which one or more offspring grows inside a woman. Labor and delivery will typically occur about 38 weeks after conception (40 weeks after the last menstrual period). The World Health Organization describes a normal pregnancy term to be between 37 and 42 weeks. Upon the initial OB-GYN visit, a woman’s doctor will most likely give an estimated due date (variable based on a sonogram) of when the child will be born. This date can also be calculated based on the woman’s last menstrual period.   While the due date is an estimate, the actual length of the pregnancy is impacted by many other factors, such as the woman’s age, length of prior pregnancies, maternal weight during delivery, etc. 1 It is likely that there are still more variables that influence normal variation in pregnancy term that are still not entirely known. Research studies have shown that less than 4% of births occur on the estimated due date, 60% of births occur within a week of the estimated due date, and, nearly 90% of births occur within two weeks of the estimated due date..

Pregnancy Detection

A pregnancy can be determined either through pregnancy tests or through the woman noticing signs and symptoms, such as missed menstruation, increased basal body temperature, fatigue, nausea, and increased urination. Pregnancy tests detect hormones that serve as biomarkers of pregnancy and can be either clinical blood tests or urine tests, with various options available. Clinical tests can indicate a pregnancy six to eight days after fertilization. Clinical blood tests are more accurate and will both detect pregnancy earlier and in smaller amounts through a test that quantitates hCG, an indicator that is present only in pregnancy and not normally in the body. Clinical urine tests are also available, but not necessarily more accurate and might be more expensive than home pregnancy tests. Clinical blood tests do assess hCG levels but take longer to evaluate, and can intercept other indicators of pregnancy if necessary (e.g., amount of antibodies to hCG).

Pregnancy Management

Numerous considerations during pregnancy, many of which are highly situational, include medication, weight gain, exercise, and diet.

Medication:

Using certain medications during pregnancy may have prolonged effects on the fetus. In the United States, drugs are classified by the Food and Drug Administration (FDA) into categories A, B, C, D, and X based on the potential benefits as well as fetal risks. Drugs with positive benefits to the mother and little risk to the fetus are classified as category A. Drugs with proven, significant risks to the fetus that outweigh any potential benefit for the mother about the drug are classified as category X.  Anyone pregnant should discuss any medications they plan to take with their doctor..

Weight gain:

Weight gain is an important and unavoidable part of pregnancy and varies from person to person, affecting several aspects of fetal development, including the weight of the infant, the weight of the placenta, the amount of extra circulatory fluid, and the fat and protein deposits of the infant. It is important to ensure appropriate weight gain during pregnancy because too little or much weight gain can negatively affect the mother and fetus, possibly contributing to an increased incidence of cesarean section (C-section) or gestational hypertension. Though these values will vary from woman to woman, the Institute of Medicine claims a total weight gain value of 25-35 pounds is appropriate during pregnancy for women who are “normal” weight (BMI 18.5-24.9), 28-40 pounds for women who are underweight (BMI < 18.5), 15-25 pounds for women who are overweight (BMI 25-29.9), and 11-20 pounds for women who are obese (BMI > 30).³

Exercise:

Research indicates that moderate-intensity aerobic exercise during pregnancy is beneficial for physical fitness and may reduce the likelihood of C-sections. Each woman’s condition varies, however, regular aerobic and strength-conditioning exercise is typically encouraged for pregnant women, and women who routinely exercised before pregnancy, along with uncomplicated pregnancies, should continue high-intensity exercise programs.4 According to the American College of Obstetricians and Gynecologists, during uncomplicated pregnancies, it would be unlikely for fetal injury to occur because of exercise. However, precaution is warranted, and a pregnant woman should consult their doctor if they experience any of the following symptoms: vaginal bleeding, shortness of breath, dizziness, headache, calf pain or swelling, leakage of amniotic fluid, decreased fetal movement, preterm labor, muscle weakness, or chest pain.5

Nutrition:

Nutrition in pregnancy is of utmost importance to both maternal and fetal health. Nutritional recommendations for pregnancy can differ from those of a person who is not pregnant due to extra energy and specifically required micronutrients.6

For example, some vitamins, like Vitamin B9 or folic acid, can help lower the risk of certain defects, while some nutrients, such as DHA omega-3 fatty acids, are needed for optimal brain and retinal development, are not as efficiently produced by infants, can only enter the infant’s body through the placenta if consumed during pregnancy or through breast milk after birth, rather than being synthesized after birth. There are many other micronutrients to help with normal fetal development as well, and there is also no shortage of information on what pregnant women are “supposed” to eat or not eat or do. All of these sources can be different to sift through, and everyone is different. The best advice is to work with your doctor or a dietitian to help you decide the best direction to go in for your needs.

1. Jukic, AM, Baird, DD, Weinberg, CR, et al. 2013. “Length of human pregnancy and contributors to its natural variation. Human Reproduction 28(10): 2848-55. PMC3777570.

2. Moore, Keith. 2015. “How accurate are ‘due dates’?” BBC, February 3, 2015. www.bbc.com/news/magazine-31046144.

3. Institute of Medicine. 2009. “Weight Gain During Pregnancy: Reexamining the Guidelines.” National Academies Press.

4. Davies, GA, Wolfe, LA, Mottola, MF, et al. 2003. “Exercise in pregnancy and the postpartum period.” Journal of Obstetrics and Gynaecology Canada 25(6): 516-29.

5. Artal, R., O’Toole, M. 2003. “Guidelines of the American College of Obstetricians and Gynecologists for exercise during pregnancy and the postpartum period.” British Journal of Sports Medicine 37: 6-12. doi:10.1136/bjsm.37.1.6

6. Lammi-Keefe, CJ, Couch, SC, Philipson, E. 2008. “Handbook of Nutrition and Pregnancy.” Humana Press.