Help... ultrasound dates!

[Singleladymomma]

Hi all, could somebody give me a clear explanation of pregnancy dating? I understand that using first day of menstrual period to date can add time on.. but I dont understand ultrasound dating?

Anyone I know (that I have spoken to) had said that their ultrasound dates match or thereabouts match when they believe to have conceived for example 5 or 6 days after sex... when either conception or implantation could occur..and when I questioned the ob/gyn he said you could have gotten pregnant later or earlier than you think, and mentioned implantation.. in fact a number of doctors have mentioned implantation leading me to believe that implantation is what they measure from.

My own gp told me when I have my dating scan done I will be able to count back. I have been dated via ultrasound measurements to have been pregnant about 3 weeks before I even slept with my (now ex) partner!
But to add to this I slept with my other ex about 3/4 weeks before the scan dates place me as pregnant. I am at a loss... do I just leave it as it is with the man I believed to be the father or do I need to speak to the other guy??
Ofcourse my ex is saying how could he be the father if I was pregnant 3 weeks before we even had sex?
I'm being torched by my mind at the moment... I have irregular periods and have not bled since sleeping with the first man... I was informed getting pregnant wouldnt be a possibility for me...now that it happened i just need to give my child the chance to know who its father is! I am torchering myself at the moment...help?!

It is mad. They count from the first day of your last period. So if that's 1st Oct, you have sex on 14th oct and get 'pregnant' then, for the first 2 weeks of oct you are both pregnant and not pregnant.... They completely changed my dates (by two weeks) after my ultrasound scan. Only thing you could try is DNA testing once the baby is here.

I think your best way forward would be to arrange a DNA test if you are not sure who the father is. It wouldn't be fair otherwise on anyone.

Essentially, pregnancy dating adds two weeks on to whenever you conceived. Most women won't know exactly when they conceived, but will know when their last period was - so that's when the pregnancy is counted from. The instant you conceive, you're two weeks pregnant. (I always yell at that stupid Clearblue advert where she's all "I'm pregnant! About two weeks!" because she would have to be literally shagging right then in order for that to be true.)

However. All this assumes that every woman has a regular, standard 28 day menstrual cycle and ovulates at day 14, which is of course not the case. So, the dating scan may tweak the dates slightly. Imagine, for example, someone who had her period on 1 January and did a positive pregnancy test five weeks later on 5 Feb - going from the date of her period, she'd then assume she was five weeks pregnant. But, perhaps she has a longer cycle and/or ovulates a bit later - so maybe rather than ovulating on 14 January, it was a week or so later and she actually conceived around 21 Jan. When she went for her dating scan, she'd be measuring a bit behind and therefore her dates would be adjusted to reflect the fact that she was actually 11 weeks pregnant rather than 12.

They don't use a completely different system of counting weeks for ultrasound than for dating from your period, though, if that's what you mean. Basically count back 38 weeks from your due date, and conception would have occurred round about then.

At our parentcraft classes, there was a couple who were asking about this as the date they had been given couldn't work as he was away abroad on that date. I can imagine it can cause all sorts of issue. I guess a dna test after baby is born would be the way to go, but maybe let both ex's know that they need to be prepared they might be a father soon.

I'm going to be interested to see what dates they gave me as I know without a shadow of a doubt when we conceived!! No judgement please but took morning after pill but it didn't work so the window is literally hours..... I'm going with an exact date in mind although keep worrying about going and having bad news as very much wanted baby now xx

@avearage same issue here. It is what it is... morning after pill wont cause any issues if you are already pregnant... although some may try to convince you it will cause baby to be abnormally developed... just a fore warning! I have experience with this issue... the hormone will not cause problems to baby...its a hormone that you have in pregnancy!

Thank u.... I have to be honest I haven't mentioned it to anyone relevant...... However keep thinking am I really pregnant stupid I know...... I've had blood work done and the normal urine test but after scan this week will feel better

@Avearage absolutely irs a very stressful time.. possibly rather exciting but ofcourse a shock too! Shock is the worst part... and it's hard to identify shock or any emotions when theres a lot going on! Everyone reassures me that it wont hit you until you have baby in your arms... but then it hits you in the most amazing way! I hope all is well with you...check back in and let me know scan went well!