How can you be pregnant without conception even occurring? Why do trimesters have such a hold on the public imagination when they mean nothing medically? What is time, anyway?
A lot of how we practice and experience healthcare isn’t about biological realities but rather is about social norms. (As a sociologist who studies health, I get to think about and write about this fact a lot.) And one great example of this fact is how we think of the timing of pregnancy.
You’ve likely heard of pregnancy as a trimester-based reality that lasts about 40 weeks. People often wait to tell the public about their pregnancies until the first trimester or the first 12 weeks are over, as the risk for loss is higher in the earlier weeks of the pregnancy. People talk about feeling better in their second trimester than in their first or third. Health websites will even give different recommendations about what foods to avoid or which exercises to emphasize depending on the trimester the person is currently in.
Guess what?
It’s all socially constructed.
In other words, society uses a way to talk about these realities that has assumptions hidden in it. And, not everyone understands those assumptions. These misunderstandings or surprises can actually change things, from legal policy to individual medical care.
First, a quick sociology lesson: all timelines are socially constructed.
Humans construct timelines to try to reflect physical realities, but even accurate understandings of realities can make for confusing and conflicting timelines. A “day” can mean a 24-hour period, the time from midnight to midnight, or the time from sunrise to sunrise or sunset to sunset. We can define when a day starts and ends differently, but each of those definitions of a day is socially meaningful. Each tells us something about the Earth’s orientation toward the sun. They are all real, but they are all socially constructed in slightly different ways.
Other timelines are also socially meaningful, even if they aren’t exactly accurate. For example, a year is ostensibly the amount of time it takes the Earth to go around the Sun once. But it’s not, really. We have to deal with that pesky extra 6 hours and 9 minutes each year (beyond the emphasized 365 days) that the Earth takes to make it fully around the Sun; hence, the creation of Leap Year, where we take four year’s worth of extra time and cram it into February 29th.
Consider how socially meaningful the 365 number is, though. We celebrate with giant parties every 365 days the important social idea of a year, even down to dropping a ball in a widely televised event at exactly the precise number of seconds required of those 365 days, even though the actual reality isn’t captured fully by this number.
Or, for a different example, consider how arbitrary time zones can be. Crossing from one city in one time zone to a neighboring city in another time zone does not mean you actually experience a massive change in your physical reality; the crops are likely the same, the sun rises at almost the same time, and the day proceeds nearly identically in these two places. However, they are technically an HOUR apart from each other.
Similarly, consider that Congress, a legislative body of the United States and the United States alone, has on occasion instituted and repealed (and then reinstituted) Daylight Saving Time. Daylight Saving Time tries to reflect a physical reality where we get different sunlight hours in summer than in winter, but the way we do it is socially constructed – in other words, it’s “made up”.
Finally, think about what year it is. This depends on whether you count from the believed birth of Christ (2025), the believed beginning of the common era (2025 – okay, no difference there), the believed creation of the world (5785), the believed travel date of the Prophet Muhammad to Medina (1446), the believed day on which the Buddha achieved parinirvana (2568), or something else. Time moves the same regardless of your point of reference; but, time is understood by different people through different societal lens.
My point is, we live our lives and perceive our experiences according to timelines, even when those timelines are variable across cultures or to some level inaccurate.
Pregnancy is no different.
The ways we measure time are constructed based on our social understandings. That’s why:
- Someone can be pregnant for two weeks before they even conceive a baby, and
- Trimesters are our main frame of reference for time in pregnancy, even though they have no medical meaning.
The potential downfall of these measurements of time is that we may think that these measures tell us about biology or medicine, when actually they may not tell us the reality about those things at all.
Pregnancy counts by weeks (i.e., “6 weeks pregnant”) start with a period, not conception.
The first two weeks or so of any pregnancy occur pre-conception and even pre-ovulation. This is because those weeks are counted since the start of your last menstrual period (LMP). In other words, you’re not actually pregnant for the first couple weeks of your pregnancy.
When someone is 4 weeks pregnant, they conceived about 2 weeks before. When a little one is “14 weeks gestational age,” they’ve actually only been around for 12 weeks. When a baby is “full term” at 37 weeks, they’re actually only around 35 weeks old. Pretty wild, right?
Trimesters were created by judges, not birth workers.
Trimesters seem like a convenient way to split up a nine month period into smaller chunks and to condense weekly milestones into bigger chunks.
But, there is actually disagreement on which week corresponds to which trimester of pregnancy (if you’re 12 weeks and 3 days, are you in your first or second trimester? Depends on whom you ask). This complication probably comes from the fact that while 9 (months) is divisible evenly by 3, 40 (weeks) is not. And we don’t have an official biological timeline of trimesters because that’s not how this concept originated. Instead, people and organizations just…pick.
The differences in trimesters don’t correspond to big leaps in embryonic or fetal development. They don’t mark particular moments of change for mom or baby. In other words, this model doesn’t reflect medical realities. And there’s a rational reason for that – it wasn’t invented by birth workers.
As far as I can tell, the concept of trimesters was popularized or possibly even invented by Justice Harry Blackmun, an associate justice of the Supreme Court of the United States of America, in his response to the case Roe v. Wade (1973). He constructed trimesters as a way to promote his view of what state restrictions were allowed to be imposed on abortion. As one legal article explains, “This trimester framework derived from the Court’s assessment of when in pregnancy each of the two recognized state interests – preserving maternal health and protecting fetal life – became ‘compelling’” (read this article for more information).
In other words, trimesters are about a potential political policy – one which has been widely debated and even revised.
Generously, we could argue that trimesters are supposed to be about viability (that the state’s interest in protecting fetal life is why Blackmun and others promoted the concept of trimesters). But, that’s actually a reason NOT to use them anymore, since our potential to keep little ones alive has changed so dramatically since Roe v. Wade was decided. Roe v. Wade’s decision stated that viability was usually possible between 24 and 28 weeks after conception: in other words, 26 to 30 weeks gestation. This corresponds to the division of 40 weeks of pregnancy into three equal parts, which would mathematically put the third trimester starting somewhere around 26 weeks and 5ish days gestation. Today, thanks to the wonders of modern science, viability can be as early as 21 weeks and 1 day gestation. So even if Justice Blackmun had been wise or correct in splitting pregnancy into three categories based on his perception of the state’s interest in the pregnancy, the changing possibilities of viability alone would call the concept of three equal trimesters into question.
Basically, “trimesters” are about U.S. politics in the 1970s. They’re not about meaningful biological realities.
(For a fascinating overview of what other divisions of pregnancy might be more meaningful, check out this article from Obstetrical and Gynecological Survey: Dating of pregnancy by trimesters: a review and reappraisal – PubMed.)
What are the implications of this?
First, people misunderstand how long babies gestate because of the whole pregnancy-dating-starts-with-a-period thing. This creates a lot of confusion about a basic reality: how we all come to be.
Second, society uses the legal-based trimester model rather than a biological model of pregnancy, which reinforces old science and non-biological understandings of biological realities.
Third, I think the emphasis on some difference in loss rates between trimester 1 and trimester 2 invites people to think that there’s a magic dropoff in their chance of loss between these two designations, when actually the chance of loss is decreasing fairly steadily between 8 and 20 weeks (for more details, check out this data tool: Miscarriage Probability Chart).
Fourth, I think people use the legal-based trimester model rather than an experiential model in situations of grief. This allows people to dismiss earlier losses, particularly first-trimester losses (the most common), as less impactful or important to people than later losses, when this may not be the case.
All in all, how we socially construct our ideas of pregnancy and time matter to how we make legal and even medical decisions. Time markers around pregnancy are a key piece of health literacy that have really fallen by the wayside. This has implications for everything from philosophical arguments about what it means to be human, to your individual medical care.
What problems or potentials do you see coming from how we “count” pregnancy? Comment below!
Abby the Sociologist Doula 
This is FASCINATING to consider!
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