Very few women actually deliver on their due date, but due dates still matter. Whether pregnancy came as a surprise or you and your partner have been planning and trying for a baby for months, a positive pregnancy test will yield an important question: How far along am I in my pregnancy? This isn’t a question Google can answer, but your doctor or midwife can help you plan the timing and make sure your baby is growing according to schedule. Turns out, estimating your baby’s due date is quite a science.
Experts say there are multiple ways to calculate how far along you are now in your pregnancy, including early ultrasounds, estimations based on later ultrasounds, measuring fundal height (the distance between your pubic bone and the top of your bump) after 20 weeks gestation, and good old fashioned counting back from your last missed period.
In fact, Dr. Eduardo Hariton, OB-GYN and fertility specialist, says going by the date of the last menstrual period is still the best way to estimate your baby’s due date. “This assumes a cycle length of 28 days, so people with cycles similar to this will have pretty accurate dating. For those with irregular or very different length cycles, however, this will be inaccurate or impossible to calculate,” he says.
Dr. Seth Plancher of Garden City Obstetrics and Gynecology says not many women are lucky enough to enjoy a clockwork cycle. A 2019 study in the journal npj Digital Medicine supports that, finding that only 13% of women have 28-day cycles. For the rest, there are other options for determining how far along you are, from early to late.