News flash: pregnancy is 40 weeks. Divide 40 by four ( ≈ four weeks to a month), and even we math novices know that equals 10. You heard it here first: pregnancy is actually 10 months! We know it’s like they just added a few more miles to the marathon once you thought you’d reached the end, but get out your Gatorade because, for some women, the race won’t end for another two weeks. Definition time: a post-term pregnancy is a pregnancy that is ≥ 42 0/7 weeks. The “start” line is first day of your last period, while a late-term pregnancy is one that falls between 41 0/7 and 41 6/7 weeks. Knowing your exact due date is super important because this will be the basis for all the D dates to come.
As OB/GYNs, we love to talk “dates.” And although we do appreciate hearing about the one you went on last night (did he or she really say that?), we want to focus on the date of your last period. The first day of your last menstrual period is probably the most frequently asked question to a pregnant woman. By the end of your 10 months (ugh, sorry to rub it in), your partner will be able to spit this number out in their sleep, it will be mentioned so many times! The reason we ask it over and over is because it determines what your due date is. It also determines if your baby is growing appropriately, if things are developing on track, and if a delivery must be planned or induced when it should or can be done.
Pregnancy and fetal development are based on “weeks.” You rarely ever hear an OB/GYN define a pregnancy in terms of months; our first and only language is weeks. Weeks of pregnancy correspond to the size and maturity of your baby’s organs, particularly the baby’s lung development. So, we will jump through hoops to make sure that your “dating” is accurate and that we know exactly how many weeks pregnant you are and how old your baby is!
Why some babies show up on time, some early, and some late is often very hard to figure out. There are risk factors for each, but most of the time, it’s sort of the luck of the draw. First-time moms, those carrying a male fetus, and women who are obese more commonly carry a baby past their due date. Additionally, if you went over with your first child, you are more likely to go the distance the second time around.
Other than discomfort and major ankle swelling, why do we care how long pregnancy continues? Well, several studies have shown that both late-term and post-term pregnancies have a higher risk of fetal complications. Factors like low amniotic fluid, stillbirth, admission to the NICU, passing meconium (babies’ first bowel movement) in the uterus and swallowing it (a.k.a. aspirating), and seizures occur at a higher rate in late-term and post-term pregnancies. In addition, the longer they cook, the bigger they get. Pregnancies that are past their due dates are more than two times likely to be macrosomic (a fancy way to say BIG!). You guessed it; a big baby is more likely to get stuck on its way out. This leads to a higher chance for an operative vaginal delivery (forceps or a vacuum) and a C-section.
So, when is it time to call it quits? A lot of this depends on your personal history: your age, how you got pregnant (fertility treatments), your medical history, your previous OB/GYN history (have you had a C-section before) and your baby’s development (size, fluid etc.). Not every delivery plan and timeline fits every pregnant woman. In most cases, labor induction cannot be planned prior to 39 weeks of pregnancy (one week before your due date). This is done to ensure that your baby is as ready as possible to take on the world when he or she makes that first appearance. While most OB/GYNs are okay with labor inductions after 41 weeks of pregnancy (the ACOG gives it the green light), they are almost all on board by 42 weeks. In fact, after 42 6/ 7weeks your baby is not only ready for preschool, but according to the ACOG, it is mandatory evacuation time.
There are ways to “get the party started,” including sex, dancing, a bumpy car ride, spicy foods, nipple stimulation (yup, we just said that), raspberry tea, and something called evening primrose oil (sounds super fancy, but really, it’s just a vaginal tablet). The cervix is the gate to the uterus. It will soften, become thinner, and ultimately open and dilate as labor gets closer. Depending on the readiness of your cervix, some of these home activities can help move the process along. Unfortunately, no matter how badly you want to meet your little one, labor often happens on its own schedule.
Once you hit the magic 40 and nothing is happening, your OB will likely initiate more fetal testing to ensure that the baby is just “chillin’ out” and is not stressed. Make sure to be in constant communication with your OB. The more surveillance you have at the end, the safer both you and your baby will be.
If things seem off (you are not feeling well or your baby is moving less), don’t stay silent. We want to hear from you, even in the middle of the night. Trust your intuition. Moms are usually right!