QuestionHi, I am 22 and pregnant with my first child. I feel like I know a fair bit about pregnancy as we lost a baby in 2006 and since then I have researched every aspect of pregnancy so much I could fill a small encyclopedia! There is one thing however that has me stuck and it's driving me insane the closer I get to my due date.
I have had a regular menstrual cycle since I was 11 years old - this is an average cycle of 28 days, give or take a couple of days either side. The longest I was ever late was 6 days, and this happened after a suspected chemical pregnancy about 6 months after my miscarriage. When we were trying to conceive this baby, I did not take note of the dates we had sex so I can't be sure when I conceived. The first day of my LMP was 11th June - and by normal calculations this would have made me due 18th March. I had no indication that month of late ovulation or any reason to believe it was not a normal cycle as usual. I went for a few scans in the very early weeks of my pregnancy due to bleeding and pain, at my first scan I was 7 weeks gone according to my LMP date, however they told me the baby would be bigger if I was that far along at the time. I went back a week later for a second scan and was told I was measuring around 6 weeks (when by LMP I would have been around 8 weeks). Consequently, the EDD given at my 12-week scan, and the date they have stuck by, is March 31st - 2 weeks after my own date by LMP. I have obsessed over this for a while, as I have read a bit about post-maturity and am concerned that if I am allowed to go to 42 weeks by their dates, I may be as much as 44 weeks by my own dates and there could be complications with the placenta etc by that point. I know the baby will come when it is ready, but it would be nice to know a more accurate due date. It also concerns me that I could go into labour earlier (by doctor dates I am now 35 weeks and have been experiencing a lot more Braxton Hicks and pelvic pressure the last couple of days) if my own dates turn out to be correct. I am sure the doctor's dates can't be right as I counted back and if they are correct, it means I conceived round about 29 days after my LMP - which by my normal cycle would be the start of my next period, not when I would ovulate. At my last appointment I was by their dates 34+3 weeks, by my own dates I was 36+2, and the fundal height was 36cm. I also had very high blood pressure at my last appointment which led to hospital tests (turned out fine) and I am worried that if it rises again, they will avoid inducing me as by their dates I could still be pre-term, even though by my own dates I am full term now.
I guess my question is this - who is right?! I know you can't tell me exactly when my baby will come, but how likely is it that either my own or the doctor's dates are accurate?
AnswerDear Claire,
Ultrasounds done in the first trimester are typically very accurate in dating pregnancies. There are certain "norms" that we have found in recent years - since we've had the ability to visualize pregnancies via ultrasound - to be fairly universal at specific weeks of early pregnancy. We can measure the diameter of the gestational sac, the yolk sac, and/or the CRL (crown-rump length) at different stages and know to within a few days the gestational age of the pregnancy.
Now, if there had been discrepancies in the results of the ultrasounds, I would say that you might have reason to doubt those results. But I am more inclined to rely on the technology at this point, since it has given consistent dating results. If it were just a matter of a doctor's calculations vs. your calculations - that would be another thing again. But this is not the case. The only data thus far that you have shared which would not be consistent is the fundal height of 36 cm at 34.5 weeks. And, though somewhat reliable for many years, I would not consider it as scientifically sound as the ultrasound technology.
Here's the thing -- it would be very rare for you to go post-dates by as much as two weeks. In fact, by 41 weeks, most doctors will start looking at induction, especially if you are having BP issues. And your baby will most likely be ready to go well before that and labor will begin on its own. If you are extremely worried about the timing of things, go ahead and discuss it with your doctor. At least that way you will know that it will be in the back of their minds should something come up.
I hope this has helped you and answered your question. I wish you well.
Brenda
