When is your
baby due?

Pregnancy Term & Due Date

Pregnancy is the period during which one or more offspring develops inside a woman, typically lasting around nine months. Childbirth usually occurs approximately 38 weeks after conception, or about 40 weeks after the last menstrual period (LMP). The World Health Organization (WHO) defines a normal pregnancy term as lasting between 37 and 42 weeks.

During a first OB-GYN visit, a doctor will typically provide an estimated due date based on a sonogram. Alternatively, the due date can be estimated from the date of the last menstrual period using Naegele's rule — adding 280 days (40 weeks) to the first day of the LMP.

While the due date can be estimated, the actual length of pregnancy depends on various factors including the mother's age, length of previous pregnancies, and birth weight. Studies have shown that fewer than 4% of births occur on the exact due date, around 60% occur within a week of the due date, and nearly 90% occur within two weeks. As such, while it is possible to be fairly confident a child will be born within about two weeks of the due date, the exact day of birth cannot be predicted with certainty.

Pregnancy Detection

Pregnancy can be detected either through pregnancy tests or by noticing physical symptoms such as a missed menstrual period, increased basal body temperature, fatigue, nausea, and increased frequency of urination.

Pregnancy tests detect hormones that serve as biomarkers for pregnancy. Clinical blood or urine tests can detect pregnancy as early as six to eight days after fertilisation. Clinical blood tests are more accurate and can detect the hormone hCG (human chorionic gonadotropin, which is only present during pregnancy) earlier and in smaller quantities, though they take more time and are more expensive than home urine tests.

Pregnancy Management

Several factors need to be considered during pregnancy, many of which are highly dependent on the individual's situation. Always consult a qualified healthcare provider for personalised guidance.

Medication

Certain medications taken during pregnancy can have lasting effects on the developing fetus. In the United States, the Food and Drug Administration (FDA) classifies drugs into categories A, B, C, D, and X based on potential benefits versus fetal risks. Category A drugs have low risk to the fetus, while Category X drugs have proven significant fetal risks that outweigh any potential benefit to the mother. Anyone who is pregnant should consult their doctor before using any medication.

Weight Gain

Weight gain is a largely inevitable and necessary aspect of pregnancy. It affects fetal development including the weight of the baby, placenta, circulatory fluid, and fat and protein stores. Both insufficient and excessive weight gain can have negative effects for mother and baby, including the need for a caesarean section (C-section) and gestational hypertension.

Based on guidelines from the Institute of Medicine (National Academies of Sciences, Engineering, and Medicine).

Exercise

Research indicates that aerobic exercise during pregnancy can help improve or maintain physical fitness and may reduce the risk of C-sections. Women who exercised regularly before pregnancy and have uncomplicated pregnancies are generally able to continue moderate to high-intensity exercise programs. However, a pregnant person should consult their doctor if any of the following symptoms occur:

• Vaginal bleeding or amniotic fluid leakage
• Shortness of breath, chest pain, or dizziness
• Headache or calf pain and swelling
• Decreased fetal movement or preterm labour
• Muscle weakness affecting balance

Nutrition

Nutrition during pregnancy is particularly important for the health of both mother and baby. Pregnancy increases energy needs and requires specific micronutrients that may not be needed in the same quantities outside of pregnancy.

Pregnant individuals should consult their doctor and/or a registered dietitian to determine the best nutritional plan for their specific needs.

References

1. Jukic AM, Baird DD, Weinberg CR, et al. (2013). Length of human pregnancy and contributors to its natural variation. Human Reproduction, 28(10), 2848–2855. PMC3777570.
2. Moore K. (2015). How accurate are 'due dates'? BBC News Magazine, February 3, 2015. Available at: 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), 516–529.
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.
6. Lammi-Keefe CJ, Couch SC, Philipson E. (2008). Handbook of Nutrition and Pregnancy. Humana Press.