Weeks of Pregnancy: A Primer

If you are going to make legislation about pregnancy, you better know what you are talking about.

Mar 19, 2024

In a recent fundraising email, Senator Tim Scott (R-SC) claimed that “Dems” will grant abortions up to 52 weeks of pregnancy. Pregnancies last 40 weeks, 42 at the longest. This is only the most recent example of a legislator spouting off about pregnancy when they know nothing about it. There is a reason you use Subject Matter Experts when you are dealing with a specific and complicated topic. Granted, there are some politicians that are doctors or nurses, but the vast majority of legislators are not Subject Matter Experts on pregnancy.

There’s a legislator in the state of Idaho, Vito Barbieri, that asked if doctors could just have women swallow a camera to see what is going on with their pregnancy. Yes, this was all the way back in 2015, but the dude is still in office. He is still influencing state policy, and he is anti-abortion. He didn’t even know that the gastrointestinal system and the reproductive system are not connected. Idaho is losing obstetricians due to anti-abortion restrictions. Three hospitals have closed their maternity units in Idaho in the last year. Obstetricians don’t want to work there because their expertise on this subject is not respected.

There are a lot of things people don’t know about pregnancy. Even women who have had children probably don’t remember the significance of the different weeks of pregnancy with relation to fetal development, unless they have had a lot of babies or are in the childbirth field. My husband and I have three children and I talk to him about this shit all the time as a doula and a nurse, but he probably can’t confidently tell you the significance of the different weeks. He does, however, know that a pregnancy lasts 40 weeks, not 52.

Once your pregnancy is over, you don’t really need to know any of this and you might actually want to focus on other things, like raising your kid or doing your job that might not have anything to do with pregnancy. I’m going to go out on a limb and assume most people’s jobs have nothing to do with pregnancy, so I think it’s worthwhile to discuss the phases.

Here are some significant facts related to the weeks of pregnancy:

First Trimester: 0-14 Weeks

Weeks 0-2, you aren’t even pregnant unless you have short cycles and ovulate early. The whole calculation of weeks of pregnancy is based on the assumption that nobody knows exactly when they get pregnant in between the first day of their last period and when they expect their next period. Some women know exactly when they ovulated and some women only had sex once in their previous cycle, so they know the earliest possible moment they could have conceived. So, the goal is to err on the earlier side.

9 Weeks: 80.79% of abortions happen by 9 weeks. (CDC, 2021)

This is what a fetus looks like at 9 weeks with all of the blood and menstrual decidua washed away.

This image is from the MYA Network. https://myanetwork.org/the-issue-of-tissue/

Weeks 10-12: During this time, you can choose to have Chorionic Villus Sampling (CVS) testing which involves taking a sample of tissue from the placenta (either with a catheter through the cervix or with a needle through the abdomen) to test for chromosomal abnormalities. A January 2024 study in the American Journal of Obstetrics and Gynecology noted that prior to Dobbs, CVS accounted for 16.7% of diagnostic procedures in Tennessee compared to 26.8% post-Dobbs. More women are wanting testing earlier, in case they decide to go out of state to receive abortion care.

14 Weeks (16 Weeks LMP): Lindsey Graham thinks that since the French have a 14-week ban, that should work for us. First of all, why do we have to model our country on France? Secondly, Lindsey Graham is 68 years old and has no children. How much do we think he knows about pregnancy? I can guarantee my husband could kick his ass in a “What do you know about pregnancy and birth?” game show. What he never mentions is that France has national health care, so not only are abortions free, but they are also easier to access. And they provide birth control for free, which is a better way to prevent abortions. And just because that is the law in France doesn’t mean that the majority of the population doesn’t want the law to be more liberal. Let’s ask some questions. I’m talking to you, reporters. And fun fact, when the French talk about 14 weeks, they mean 14 weeks since conception which is 16 weeks since your last menstrual period, which is how we measure weeks of pregnancy in the U.S. Again, reporters, I haven’t seen this mentioned when any of you report on Lindsey Graham’s desire for France’s abortion policy to be a model for us. Also, in France, there are exceptions for fetal anomalies and the health (mental and physical) of the mother that allow abortions after 14, or rather 16 weeks. Why can't we model ourselves on the Netherlands? Abortion is legal there for any reason up until 24 weeks.

Second Trimester: 15-28 Weeks

15-16 weeks: There has been an argument by anti-abortion groups that the fetus feels pain at 15-16 weeks. This is not true. According to the American College of Obstetricians and Gynecologists (ACOG), this does not happen until after 24-25 weeks.

15 weeks: This is the point in a pregnancy that Virginia Governor Glenn Youngkin (R) proposed for an abortion ban. He called it a limit or consensus, but wtf is the difference? I think he just thought…..”hey, it’s currently 24 weeks in Virginia and people are whining about 12 weeks, so lets come up with something in the middle.” Nevermind that it might have some significance as to when fetal anomalies are discovered. Again, what exactly do legislators understand about pregnancy?

16 weeks is very significant in terms of pregnancy testing. The Alpha-Fetoprotein (AFP) blood test can identify a higher risk for Downs’ Syndrome or other genetic anomalies. This test is only accurate if it is done very close to 16 weeks. So, if the results are off, your provider can do an ultrasound to measure the fetus and see if your dates seem correct. If they seem correct, they will advise you about amniocentesis, a test where a needle is inserted into the womb to extract some of the amniotic fluid to be used for genetic testing. It is your choice whether you get this test or not. The AFP test is not very accurate due to the dependency on dating of the pregnancy, but amniocentesis is very accurate.

16-20 Weeks: If there are no issues with the AFP test, if you chose to have it, this is around when most ultrasounds are performed to looks at all kinds of different things on the fetus, and measures body parts and look for a penis if you want to know the sex. So 16-20 weeks is very important in terms of identifying issues with the fetus.

20 weeks. A significant point to make about 20 weeks is that 99.15% (CDC, 2021) of abortions occur by 20 weeks. So, less than 1%, or 0.85%, of abortions happen after 20 weeks and a lot of those happen close to 20 weeks because a problem has been identified in the 16-20 week timeframe and it took until after 20 weeks to access care. Or, the pregnant individual had a hard time getting an abortion or raising the money for an abortion until this point.

24 weeks. This is around the point of viability. This is the point where a baby could survive outside of the womb, albeit probably with significant medical intervention. Not all babies are viable at 24 weeks because they all develop at different rates.

Third Trimester: 29 to 40-42 weeks

37 Weeks: The general term “Term” refers to anytime after 37 weeks. The baby should be ok if born anytime after 37 weeks. The weeks are broken out further, so that providers can address things that might occur closer to 37 weeks or closer to 42+ weeks.

37-39 Weeks or “Early Term” if your baby is born between 37 weeks, 0 days and 38 weeks, 6 days. 37 weeks is also the point when women stop holding their breath hoping everything is ok and then patiently (or not so patiently) wait for their baby to decide it is time to come out. With your first baby, you start looking at your watch as soon as you hit 37 weeks, expecting something to happen at any moment. With your third baby, you plan on being pregnant for another 4 weeks.

39-41 Weeks or “Full Term” if your baby is born between 39 weeks, 0 days and 40 weeks, 6 days.

41-42 Weeks or “Late Term” if your baby is born between 41 weeks, 0 days and 41 weeks, 6 days. When you hear the term “late-term abortion,” know that that is not a thing. It would be more accurate to say a “later” abortion or a “third trimester” abortion, but late-term means you are pregnant beyond 41 weeks. Nobody has abortions this late in pregnancy. It’s not a thing. If there is something wrong with the baby or the mother this late in pregnancy, an induction takes place and the baby is born and given appropriate medical attention.

42 Weeks+ is “Postterm” if your baby is born after 42 weeks, 0 days.

So, my friends, these are the significant events according to weeks of pregnancy. If you don’t understand all of this, then you should not be making policy decisions that impact other people. You should be consulting with a Subject Matter Expert, like a doctor or a midwife, to understand the best policy on abortion. This is what women want to do, consult with a doctor or a midwife, regarding their decisions about their pregnancies and their bodies, not their elected representatives.

And as usual, shout out to my favorite sub stacks: