How Many Months Pregnant Am I?

Woman lying on futon holding her pregnant belly
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The average pregnancy lasts 40 weeks from the day of the last normal menstrual period. Most physicians and midwives use the gestation calculation of weeks rather than months because it is more specific.

Answer: We talk a good game about having nine months of pregnancy. But if you look at it mathematically, there are an average of 40 weeks in a normal pregnancy. If you calculate a month as being four weeks, that makes 10 months of pregnancy in every 40 weeks.

The problem with this calculation is that it has 28 day months, which is not the norm in our calendar months.

There is also the issue of when you actually are pregnant. Now this honestly doesn't really matter much to most people, since that's just how pregnancy is calculated. And, by the time you have a positive pregnancy test, you are four weeks pregnant. Here are some common breakdowns of the months of pregnancy and their explanations:

Heavy on the 1st Trimester

  • Month One: Week 1-6
  • Month Two: Week 7-11
  • Month Three: Week 12-16
  • Month Four: Week 17-20
  • Month Five: Week 21-24
  • Month Six: Week 25-28
  • Month Seven: Week 29-32
  • Month Eight: Week 33-36
  • Month Nine: Week 37+

This set of weeks assumes that early pregnancy is very important but that you aren't really pregnant those first two weeks.

Heavy on the 3rd Trimester

  • Month One: Week 1-4
  • Month Two: Week 5-8
  • Month Three: Week 9-12
  • Month Four: Week 13-16
  • Month Five: Week 17-20
  • Month Six: Week 21-24
  • Month Seven: Week 25-28
  • Month Eight: Week 29-32
  • Month Nine: Week 33+

This set of weeks counts every moment from the last normal menstrual cycle and considers the fact that some women have their babies earlier than 40 weeks.

So, as you can see, there are not a lot of solid answers as to the right way to count months of pregnancy.

So the next time you are asked: How many months pregnant are you? You will know that you can safely answer, just about any month you feel is appropriate for your gestational age. 

Since your doctor or midwife don't count in months, there is very little ramification for your answer, nor need for justification for the answer. Counting by weeks is what your practitioners will use. This helps them more accurately figure out how far along you are and therefore, what they should be seeing in terms of the health of you and your baby. So the next time you are in for a prenatal visit - be sure to ask for your practitioner's take on the weeks versus months debate.

Interested in figuring out when you got pregnant? Try the backwards pregnancy calculator.

Source:

Obstetrics: Normal and Problem Pregnancies. Gabbe, S, Niebyl, J, Simpson, JL. Fifth Edition.

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