Just had a scan - how accurate are the dates?

[Georgeoftheinternet]

Just had my scan and they are saying I’m 6 weeks plus 2 days. I had sex on the 20th and 25th of September. So just trying to work out which date would be the most likely conception date?

What date was your last period? How often do you normally ovulate?

I would say your more likely to have caught on the 20th as 6weeks 2days take you back to the 19th I believe. But when was your last period as they say you ovulate about two days after that.

Two week * 🤦‍♀️

I would say 25th is more likely given your dates, but you can't really be sure.

I counted back 4 weeks and 2 days as the first 2 weeks of pregnancy are pre ovulation, so that's my best guess.

When was your LMP?

Dates are much more accurate later on, that early they can put you a week ahead or behind incorrectly and then at 12 weeks it will have caught up.

I was dated at 5.5 weeks when I knew I was 6.5 weeks but by 10 weeks, I was measuring exactly right again.

Is it important to know which day conception was?

But when was your last period as they say you ovulate about two days after that.

That’s not correct, especially as period length and cycle length varies dramatically. I have 21 - 26 day cycles and 8 -10 day periods usually which means some cycles I ovulate before my period has finished. Most women will ovulate a week or more after their period has finished. Women generally ovulate around 14 days before the start of their next period no matter their cycle length. So if your cycle is 28 days, you’ll ovulate about 2 weeks after the first day of your period. If your cycles are irregular, it’s impossible to know when you ovulated without knowing when your next period would have started.

Pregnancy dates assume a 28 day cycle.

It’s not possible to say which date you conceived because sperm can live inside the body for a few days. So you could have ovulated and conceived from the first encounter any time in the 4 intervening days, or you could have ovulated after the second time.

Generally, deduct 2 weeks off the dates given which means likelihood is you conceived 4 weeks and 2 days ago which would be 26th September. However, there’s no way to know for sure with dates so close together. Generally early scans are pretty accurate but there’s no way to know for sure. You could have actually conceived on the 24th or 25th September from the first encounter. Really depends when you ovulated.

Based on those dates, you likely conceived (ovulated) on the 26th September as the first 2 weeks of pregnancy are before you actually conceive. It comes from a typical 28 day cycle so your date of last period isn't really much use unless you know how long that particular cycle was - mine is usually 31-33 days but the cycle where I conceived it was 26 so I would have been well out using my average.

Sperm can live up to 5 days so it's unlikely but not impossible to be from the 20th, especially if you had sex in the evening and ovulated early in the day.

It honestly could be either. Depends how long your cycle is, how regular it is, when you ovulated... I have regular 28 day cycles but have ovulated as early at day 10 and as late as day 18. Sperm can live up to 5 days to meet an egg that comes for 24 hours. Foetuses also don’t grow at the exact same rate, measuring 6+2 doesn’t mean you necessarily got pregnant 6+2 weeks ago. Im pregnant and know exactly when I ovulated, but baby has measured 5 days bigger the entire pregnancy.

So without knowing when you ovulated, 2 options 5 days apart could both be possible.

I have/had PCOS and my periods are all over the place. They were somewhat regular at 28 days but I’m not suggesting you use that as I didn’t keep a log etc.
Two different fathers :/

There’s not going to be any way to know for sure; or even have a strong idea, until you get a DNA test. It’s just too close to call. I believe you can get some DNA testing during pregnancy, but it’s easier and less risky once the baby has been born.

You haven’t said if you’re happy, but I hope you’re doing okay either way

@ShellsAndSunrises thank you. I’m not sure, as it’s now someone else I have to contact :/

You aren't going to know until a dna test is done. Do you feel safe letting both men know? You aren't obligated to do that.

I’ve told one and he’s ghosted.

Id say 25th.

But yes youll need dna test.

Is there a reason you had an early scan?

Going from when I had my last period I measure 8 days behind

I would say 25th if you generally have a 28 day cycle.

Hey everyone.... I didn’t want to use a 28 day cycle as I don’t know for sure.

@FallonCarringtonWannabe for a termination. Not sure if it’s allowed to be posted here.

I had a strong pregnancy test line 12 days after sex and the pregnancy test said 2-3 weeks so I don’t think it can be 25th.

[quote Georgeoftheinternet]@FallonCarringtonWannabe for a termination. Not sure if it’s allowed to be posted here.[/quote]
If you click on "report" on your own opening post, you can ask MNHQ to move the whole thread to antenatal choices which might be more suitable.

In answer to your actual question, I don't know about 6 week scans, but at my 12 week scan they insisted on moving my dates by a week, despite me having had IVF and thus knowing exactly when I conceived. DS was born bang on 40 weeks according to their dates, a week late according to mine - and as the midwife commented, definitely had that "too long in the bathwater, wrinkled like a prune" look. So they can certainly be out by at least a week.

@CaraDuneRedux wow, what was your response to your DNA statement

Their response*