# Calculating months in pregnancy

OK, can someone help me out here. I’m finding the whole thing a little confusing. Some books and websites list each month of pregnancy as 4 weeks long (making pregnancy 10 lunar months). Calculating this way, I am starting my 6th month of pregnancy. Others break it down more specifically. The Dr. Sears books, which I’ve been using throughout my pregnancy, break it down into 9 months. For example, I’d be in my 5th month right now, which is listed as between 17 and 21 weeks, 21 weeks being the starting point for the 6th month. Maybe this is a goofy thing to be concerned about, but I find it confusing! And I can’t mark my day-planner with my months of pregnancy if I don’t even know them, darnit! The various books and websites don’t even agree as to when trimesters end and begin. Some say the second trimester ends on the 24th week, others the 26th or 27th. Aarrgh…… So can someone simplify this for me, please!? :whacky: Thanks!

[quote=MooCowSteph]OK, can someone help me out here. I’m finding the whole thing a little confusing. Some books and websites list each month of pregnancy as 4 weeks long (making pregnancy 10 lunar months). Calculating this way, I am starting my 6th month of pregnancy. Others break it down more specifically. The Dr. Sears books, which I’ve been using throughout my pregnancy, break it down into 9 months. For example, I’d be in my 5th month right now, which is listed as between 17 and 21 weeks, 21 weeks being the starting point for the 6th month. Maybe this is a goofy thing to be concerned about, but I find it confusing! And I can’t mark my day-planner with my months of pregnancy if I don’t even know them, darnit! The various books and websites don’t even agree as to when trimesters end and begin. Aarrgh…… So can someone simplify this for me, please!? :whacky: Thanks!
[/quote]

40 weeks. Go by weeks, it’s less confusing.

[quote=jrabs]40 weeks. Go by weeks, it’s less confusing.
[/quote]

But then when people say, “how many months are you?”, I just don’t know what to say. I said today that I’m almost 6 months, and then mentioned that I’m halfway through, and got all kinds of confused looks!

Very confusing. My wife just found out that she is pregnant with our second child, and trying to calculate even the weeks is confusing. Someone told her that you have to calculate from the first day of your last period… huh? How does that make any sense?

Yep, this confused the heck out of me with #1. Doctors and other pregos will understand if you give weeks, but the general populace still believes that pregnancy= 9 months, and there are 4 weeks in a month. So, if you say you are in your ninth month, you are 36-40 weeks along. So if you are in the 0-4 weeks month, you aren’t really pregnant to the average person! Confused enough? Then try looking at some baby website calenders. Many will give you two different week designations. Weeks, and weeks LMP (from your last menstrual period) The average person also doesn’t consider (or really care usually) that you could be at the very begining of your 8th month, or at the end of your 8th month. They are mostly just being polite, so anything relatively close is usually good enough, and as an engineer I have to tell you that good enough really is. (Sorry, that’s a process control/cost thing.)

Hi Steph,

I am 17 weeks so I figure I’m (almost) starting my 5th month. This is how I’ve worked it out… (I’m due Jan 26)
(The number on the left is the week of pregnancy that starts the month)
18) Aug 27 - Sept 26 …my 5th month of pregnancy
23) Sept 27 - Oct 26… 6th month
27) Oct 27 - Nov 26… 7th month
31) Nov 27 - Dec 26… 8th month
36) Dec 27 - Jan 26… 9th month

So start with your due date and work backwards… Since the month change isn’t the same as the week change - I just round to the nearest week.

It is confusing as the first day of a woman’s last menstrual period (LMP) is week one . And total gestational period for a woman is 40 weeks. Go figure! I work in the birth center at my hospital, and we have these neat little" wheels" that tell us weeks/trimesters/ and months…makes it all a whole lot easier!
~ Kathy ~

[quote=carol marie]Hi Steph,

I am 17 weeks so I figure I’m (almost) starting my 5th month. This is how I’ve worked it out… (I’m due Jan 26)
(The number on the left is the week of pregnancy that starts the month)
18) Aug 27 - Sept 26 …my 5th month of pregnancy
23) Sept 27 - Oct 26… 6th month
27) Oct 27 - Nov 26… 7th month
31) Nov 27 - Dec 26… 8th month
36) Dec 27 - Jan 26… 9th month

So start with your due date and work backwards… Since the month change isn’t the same as the week change - I just round to the nearest week.
[/quote]

This is how I did it too- took my due date and counted backward by the month, and this is what I would tell people. I counted it by the week, myself- it made it seem like I was making more progress!

[quote=carol marie]Hi Steph,

I am 17 weeks so I figure I’m (almost) starting my 5th month. This is how I’ve worked it out… (I’m due Jan 26)
(The number on the left is the week of pregnancy that starts the month)
18) Aug 27 - Sept 26 …my 5th month of pregnancy
23) Sept 27 - Oct 26… 6th month
27) Oct 27 - Nov 26… 7th month
31) Nov 27 - Dec 26… 8th month
36) Dec 27 - Jan 26… 9th month

So start with your due date and work backwards… Since the month change isn’t the same as the week change - I just round to the nearest week.
[/quote]

This makes a lot more sense! Thanks! I’m going to count them out on my calendar right now

I’m 31 weeks. That means I’m just going into my 7th month.

At least that’s what the doc said

I always go by weeks. I delivered my oldest at 31 weeks, my second at 36 weeks, my third at 37 weeks and now my fourth…well we’ll see when they take the cervical stitch out at 36 weeks when I’ll have this one.

People who want to know in months how far along…I tell them there’s 40 weeks in a pregnancy, I don’t have the luxury of going month by month. The closer I get to 40 weeks, the better for the baby.

But that’s just me

40 days, 40 nights and 40 weeks and 40 years. Coincidence? Interesting.

I’d think about it like age. When a baby is born, he begins his first year - at the end of that year, he is one year old and in his second year. When you complete your first 4 weeks, you are in your second month. When you complete your 12th week, you are in your 4th month,

[quote=buffalo]40 days, 40 nights and 40 weeks and 40 years. Coincidence? Interesting.
[/quote]

I never thought of that!

40 is often understood as the number of probation or trial…How interesting indeed!

When I was in my Maternity Nursing course, I spent some time playing with the number to understand it better. I am not sure I was successful, but this is what I calculated. Pregnancy lasts 40 weeks (280) from the LNMP (last normal menstrual period) or 38 (266) weeks from ovulation. Using 40 weeks, pregnancy lasts 10 lunar months (lunar month = 28 days) or 9 ½ TRUE lunar months (true lunar month = 29 ½ months) or ~9 calendar months (calendar month ~ 30 ½ days). Using 38 weeks, pregnancy lasts 9 1/2 lunar months (lunar month = 28 days) or ~9 TRUE lunar months (true lunar month = 29 ½ months) or ~8.7 calendar months (calendar month ~ 30 ½ days). Most people are interested in the calendar month. You can calculate this by counting how many days pregnant you are and dividing by 30 1/2.

I think the simplest method is to add one week to teh LNMP period and then count the months from there. My LNMP was 10/13 with my son, so my EDD was 07/20 (actually 07/19 b/c it was a leap year). When adding one week to my LNMP and counting 9 months you get 07/20.

[font=Book Antiqua]If you know when you ovulated, just account for that difference. [/font]

Someone told her that you have to calculate from the first day of your last period… huh? How does that make any sense?

This is because more women know their LNMP than their date of ovulation.

I hope I didn’t confuse things.

Autumn

[quote=Katie1723]It is confusing as the first day of a woman’s last menstrual period (LMP) is week one . And total gestational period for a woman is 40 weeks. Go figure! I work in the birth center at my hospital, and we have these neat little" wheels" that tell us weeks/trimesters/ and months…makes it all a whole lot easier!
~ Kathy ~
[/quote]

With my first, the nurse read the wheel wrong and told me my baby was due a month earlier than what it was supposed to be. Oh yes, and I told my family I was pregnant before figuring it out myself, then got all sorts of questions because we had just gotten MARRIED! My family was telling me that if that were true I was pregnant before I was married. Lord, was that a mess.

DISCLAIMER: The views and opinions expressed in these forums do not necessarily reflect those of Catholic Answers. For official apologetics resources please visit www.catholic.com.