Calculating conception

selenas1997 · September 2022

Hello, I’m actually currently pregnant. In my 3rd trimester. And Im struggling with the conception dates.

I had a period in November 7th to 13th

A period in December from the 10 to 16,

sex in December on the 17 and 23rd.

No period in January.

Sex on January 24th and 25th

Negative test February 5th

Positive test February 11th

An ultrasound February 22nd to confirm pregnancy and was dated at 5 weeks and 5 days.

An ultrasound March 15th and was dated 8 weeks and 4 days.

At 33 weeks I was told my baby is measuring 3 weeks ahead.

My fundal height has been very close every appointment though. Measuring right on track.

So which day do you likely think I conceived? In December or January?

Update/ at my 36 week check up I was told baby is measuring 41 weeks. A 2nd glucose test was done last week and I’m prediabetic.

I’m worried because at 36 weeks they mentioned baby’s lungs are not strong, but they think because she’s so big I will deliver sooner. Do you think it’s possible she’s an older gestational age? Doctor said because we measured baby so early (5w and 5d) that my due date is most definitely accurate. My fundal height today was 41 weeks. I’m very worried about delivering such a large baby if I wait longer, but also worried about delivering before she’s ready.

inthewoods23 · September 2022

Early ultrasounds are much more accurate compared to 3rd trimester ultrasounds. Baby may just be in a higher percentile. You should discuss your concerns with your doctor.

Wishilivedinflorida · September 2022

Your doc is right. The earliest measurements have less margin of error and are most accurate for dating. If you conceived in December your pregnancy test on Feb 5th would have most definitely been positive. You probably just have a large for gestational age baby. Keep in mind that later ultrasounds can be off by whole pounds. But if they are concerned you need some intervention, they will let you know. Babies born at 36+ weeks do well in general. It’s not ideal and it’s scary, but not worst case scenario.

coldlife2 · September 2022

At 33 weeks you were told the baby was measuring ahead based on what? Since your fundal height is right on.

U/S estimates of baby size at late stages are crap, and I think it’s criminal how much doctors rely on them these days and use them to scare women into interventions that often are not necessary.

Here is a link to the ACOG’s guidance on suspected large babies. Unfortunately, it is no longer available without paying for it (boo, this sort of thing should be available), but here is the link anyway, and my summary from a prior post when I was able to view it. Please especially note the second point.

https://journals.lww.com/greenjournal/Fulltext/2020/01000/Macrosomia__ACOG_Practice_Bulletin,_Number_216.50.aspx

-If a provider tells you your baby is estimated at greater than 9 pounds, 15 ounces, that estimation is wrong more than half the time (first paragraph under "Diagnosis.")
-A physical exam (aka - feeling your belly and measuring fundal height) is about as accurate as ultrasound (last paragraph under "Diagnosis.")
-Suspected macrosomia is not a reason to induce prior to 39 weeks (under the question that starts "is there a role for induction of labor...").
-A planned c-section due to suspected macrosomia is controversial, and generally isn't recommended unless the baby is estimated at more than 11 pounds. Even then, it should be a discussion between the woman and her provider, including noting that ultrasound estimation is notoriously wrong (and, as referenced above, that it's wrong more than half the time at this weight) (under the question that starts "when should scheduled cesarean birth...")
-A suspected big baby is not a reason to skip attempting a VBAC and going straight to a c-section (under the question that starts "is suspected macrosomia a contraindication...")

Calculating conception

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