what is with this 9 months business?

[HeartsOpenWide, RN]

So full term pregnancy is 40 weeks, but why do they always refer to 9 months? Do they just round since 40 weeks is calculated by the last LMP and actual date of conception can not be determined?

[nicuRN2007]

It's because each month (except for Feb) is a little over 4 weeks making 40 weeks closer to 9 months than 10 months. For example...if my LMP was Jan 1, using Naegele's Rule and the 40 weeks from LMP rule, my due date would be October 8. Jan 1 to October 8 is just over 9 months. Hope this helps!

[SmilingBluEyes]

We ought refer to "lunar months" when discussing pregnancy---and truly it's 10 lunar months. I think it also a throwback to the fact most don't know they are actually pregnant til they are a few weeks along, and conception was not always so easy to pin down as to when it happened. Old habits die hard.....

Actually getting techincal, it's best to go by weeks' gestation, anyhow, to avoid all confusion.

[mom23RN]

I always thought it was because those first couple of weeks that they consider gestation you're not actually pregnant (considering you ovulated about 14 days after the start of your last cycle).

[shortstuff31117]

I agree its easier to go by weeks. And you ovulate 12-16 days before the start of your next cycle, not 14 days after the end of your last one. This is why the pregancy wheel is not accurate for most women - since its based on a 28 day cycle.

[cardiacRN2006, ADN, RN]

I always thought it was because those first couple of weeks that they consider gestation you're not actually pregnant (considering you ovulated about 14 days after the start of your last cycle).

Actually, technically, you are pregnant at the begining of each period until you ovulate. Then, your pregnancy only continues if fertilization is achieved.

I agree its easier to go by weeks. And you ovulate 12-16 days before the start of your next cycle, not 14 days after the end of your last one. This is why the pregancy wheel is not accurate for most women - since its based on a 28 day cycle.

Thank You!! Finally, someone who understands the luteal phase! Yes, the wheel would never be accurate for me if I were to ever get pregnant.

[KellNY, RN]

It's easier to go by weeks when you're talking with someone who knows about pregnancy (ie in the medical field, self educated, or took childbirth classes).

I remember when I was pregnant and a stranger would ask how far along I was, I'd say, for example, 26 weeks. I'd get a "Huh? No, I mean, how many months pregnant are you?". Even on the unit I work for, I'll mention their gestation in weeks and they'll look at me like I have a frog growing out of my nose.:uhoh21: