All About the First Trimester

For most women, the first 12 or so weeks of pregnancy are the most consuming because everything is all so new, so exciting, even overwhelming. To satisfy the little voice inside your head that keeps asking questions, here's a primer. Keep it handy.

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Aversions (and cravings)
Being repelled by certain tastes and smells is common. “Your digestion is slowing down, so some formerly appealing foods become intolerable,” explains certified nurse-midwife Lisa Kane Low, Ph.D., R.N., a faculty member at the University of Michigan School of Medicine. Ignoring an aversion may only make you feel sicker, so don’t feel you have to eat something just because you think it’s good for you. Cravings are the flip side of aversions: Although the cause is unknown, they may simply be your body’s way of telling you to eat what you can stand. Unless they could be harmful (see “H”), go ahead and indulge them.

Breasts
“Pregnant women always think of their bellies as the focal point,” says Low, “but usually the first physical symptom they notice is a too-tight bra.” In fact, the symptoms of early pregnancy, such as acne, mood swings, cramps and especially swollen, tender breasts, closely resemble PMS.

Chorionic Villus Sampling (CVS)
This diagnostic test for chromosomal disorders such as Down syndrome is usually performed between weeks 10 and 12. CVS can be done earlier than amniocentesis, but unlike amnio, it cannot detect neural-tube defects such as spina bifida. In addition, says Donald R. Mattison, M.D., senior adviser to the directors of the National Institute of Child Health and Human Development and Center for Research for Mothers and Children, the miscarriage risk is slightly higher with CVS—around 1 percent vs. less than 1 percent for amnio.

Due date
Pregnancy is based on a 40-week (280-day) calendar. To calculate your estimated date of delivery, add seven days to the first day of your last normal menstrual period, then add nine months. Your baby is considered full term if he arrives anywhere from three weeks before to two weeks after this date (more than 90 percent of babies do). If your menstrual cycle regularly is 28 days long, you’re more likely to give birth near your due date. If your cycle is usually longer than 28 days, you’re more likely to deliver later; and if it’s shorter, earlier. But the most accurate way to date a pregnancy is via ultrasound measurement of the fetus’s crown-to-rump length between eight and 12 weeks.

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