My lovely pregnancy ticker over on the right is based on my Estimated Due Date of 4/19/11. However that would be remarkable for a twin pregnancy. I’ve recently been researching twin gestation to help plan my maternity leave – something that is difficult with all the unknowns of pregnancy under normal circumstances. Here’s what I’ve learned so far.
40 weeks is the “due date” for most women because it is the average length of gestation for singleton pregnancies. For twin pregnancies the average length of gestation is 36 weeks. For me that would be March 22, 2011 instead of April 19, 2011 – a whole month earlier. But it isn’t as simple as planning for delivery pretty much around a certain week. As you can see in the graph to the left[1. A parsimonious explanation for intersecting perinatal mortality curves: understanding the effect of plurality and of parity] (click to view larger) twin pregnancies have a different shaped curve than singleton pregnancies. More than 30% of all singletons are born in week 40 and approximately 65% are born in the week before and after. Twins on the other hand, although averaging 36 weeks, only about 20% will deliver this week. With a sharp decline you can see that very few (approximately 6%) twins are born after 39 weeks.
Now, in the natural parenting community it is highly desirable to “let nature take its course” and not be pressured by “due date” inductions of labor or threatened c-sections. I felt this way about Aellyn’s birth. Should I feel the same about the birth of my twins? The chart to the left shows the incidence of stillbirths in singleton and twin pregnancies. Although OBs often try to scare mothers into induction due to stillbirth you can see that the “increased risk” is very minimal. While these numbers aren’t huge with twins either (up to 8%) it is significant to me how steep the change is. While twins develop a little earlier they really don’t benefit from an extended stay in the uterus[2. Mortality of Twins and Singletons by Gestational Age: A Varying-Coefficient Approach]. A push for induction after 38 weeks is not as aggressive on the part of the OB as (I feel) it is with singletons. In my opinion it is prudent.
What can I glean from this? First, my goal is 36 weeks. While singletons are not premature at 38 weeks (two weeks earlier) and generally no one would stop labor at that point; twins born at 34 weeks is way too early. The same two week window that exists around a singleton, 40-week due date does not hold for twins. I don’t want to deliver before that 36 week mark (and certainly not before 34 weeks which is a crucial juncture for lung development). Second, I am highly unlikely to still be pregnant after 38 weeks and would accept induction at that time as my risk for stillbirth increases after that point. So…
My due date is between March 22 and April 5, 2011.
Or, in the next 67 to 81 days. Not the 98 days that mr. ticker over there is saying.