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Due date / conception date help needed

(15 Posts)
jakesmith Sat 06-Dec-14 12:39:36

My DW took her last pill on Friday 3rd Oct. We had sex on the 4th. We didn't have sex again till 3 weeks later. Obviously she didn't have a period between coming off the pill & us havig sex 1 day later but she was having a very slight bleed from Thursday 2nd at the time.
She is now pregnant and that is the only date she could have conceived so is it OK to time the scans etc from this conception date plus maybe 2-3 days, as the midwife, consutant midwife & sonographer could not understand that she could not be 11 weeks pregnant & wanted to add 2 weeks onto the conception date
We are completely confused by this as she can't have got pregnant before coming off the pill

bluetrain Sat 06-Dec-14 13:04:38

two weeks is always added on before the conception date. it's because of the assumption that she'll have had a period two weeks before ovulation and she'd have concieved at ovulation. a pregnancy is dated from the first day of your last period.

for a rough example - woman starts period on the 1st of a month, has sex on the 13th of that month, ovulates on the 14th of that month then gets a positive pregnancy test on the 28th of that month = 4 weeks pregnant (but only two weeks since conception)

Cariad2014 Sat 06-Dec-14 13:20:19

As Blue says - the NHS will always date your pregnancy from the date of your last period - which in your wife's case sounds like Thursday, 2 October. This means that the first 2 or so weeks of any "pregnancy" will be time before you actually conceived. I've had two early pregnancy losses in the last 6 months and each time the hospital dated them from the date of my last period (and not when I conceived).

I would definitely go on the dates given to you by the sonographer. Where a cycle is any longer than 28 days (and it sounds like your wife's may have been), the scan is used to accurately date the pregnancy - this has happened to quite a few friends of mine recently - one was a week and a half less pregnant than she thought she was and the other was a week and a half more pregnant.

jakesmith Sun 07-Dec-14 08:00:14

Thanks for this but how can she be 2 weeks pregnant when she was on the pill and we didn't have sex. If gestation takes 40 weeks how can this not be timed from when the egg meets the sperm. Sorry I'm sure I come across as being a bit thick but I'm not doing it on purpose it doesn't make sense to us and we want to make sure we have the screening done at the right stage

butterflycats Sun 07-Dec-14 08:07:40

As others have said... It's not dated from when sperm and egg rmeet, it's from the first day of your last period, so for your other half, the day she came off the pill, as this is when her body started getting ready to release the egg that was then fertilised. They will measure baby on the day to make sure it fits in with the dates, and with screening tests. Hope this helps

jakesmith Sun 07-Dec-14 08:13:31

She came off the pill the one an only time we had sex. Last pill taken Friday 4th, had sex sat 5th. No period before as was on the continuous pill. Really don't get biologically how she could have been 2 weeks pregnant and the 3 people we spoke to in the hospital all told us different things. This is supposed to be a happy time and we're both just really confused

skitter Sun 07-Dec-14 08:17:07

It's confusing, but pregnancies are dated from the first day of the period before conception (ie when you are not actually pregnantand may still be using contraception). In yourq case, as there was no period before conception the health workers will just add two weeks before the assumed date of conception to get an approximate due date. This date will likely be changed after the 12 week scan, when they'll measure the baby and get a more accurate date (this change of due date after the 12 week scan happens in many pregnancies). The 40 weeks of pregnancy don't start on the date of conception, which generally occurs around 2 weeks, give or take, after the start of a period. The 40 weeks start from day 1 of the period before you actually conceive. If you date from conception you only need to count 38 weeks (but most people don't know exactly when they ovulate and therefore can't pinpoint conception as the sperm can survive in the body for many days).

elpth Sun 07-Dec-14 08:18:19

Gestation is timed (on average) as 38 weeks from when egg met sperm. The 40 week gestation comes from assuming that all women ovulate two weeks after their period starts and have 28 day cycles (not always the case). So if you know the date of conception, add 38 weeks to that to get a due date. Though there is a lot of variation in average gestation so don't expect the baby to turn up on its due date!

RainyLion Sun 07-Dec-14 08:30:34

yes like everyone is trying to say, all pregnancies are measured from the date of the last period which is typically 2 weeks before you actually conceive (if you ovulate on day 14). This is because most women don't know or can't be sure when they actually conceived but they do know when their last period was, so it is easier to date. So for example I am 8 weeks pregnant but I actually conceived approx 6 weeks ago. So when we say pregnancy lasts 40 weeks it is actually only 38. Although obviously most babies don't actually come on their due date. So if the midwife etc are adding 2 weeks they are not actually saying you conceived 2 weeks earlier they are just taking into account that in a normal cycle (no on the pill) your wife would have had a period 2 weeks before she conceived.

jakesmith Sun 07-Dec-14 08:45:50

Ok I finally get it! (I think) Thanks everyone.

jakesmith Sun 07-Dec-14 08:55:56

Oh so when should we be 12 weeks for the purposes of scans? 12 weeks from conception or 10 weeks from conception?

jakesmith Sun 07-Dec-14 09:53:41

Guys last question please!!

53Dragon Sun 07-Dec-14 09:54:53

10 weeks (roughly) from conception

53Dragon Sun 07-Dec-14 09:57:34

I speak as someone who meticulously planned the arrival date of her first child... Knowing that you're pregnant for 40 weeks I worked out the earliest date to conceive to make the due date a couple of weeks after Christmas. Got pregnant first time then found out that 40 weeks took me to New Year's Eve!! Ds1 will be 21 on 27th Dec grin

RainyLion Sun 07-Dec-14 10:12:57

scan would be 10 weeks from conception but you don't always have your 12 week scan bang on 12 weeks anyway. It's possible to date pregnancy from 10-14 weeks so it will be anytime inbetween.

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