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When Did I Likely Conceive?

I found out June 10 by a Transabdominal ultrasound I was pregnant they assumed it was around 5 weeks and 2 days due date 2/8 only gestational sac and present yolk sac. I went back on June 26 and had a transvaginal ultrasound which measured me 7 weeks 6 days due 2/6 and a CRL of 16.8. My anatomy scan was September 19 and I had an EDD (estimated due date) of 2/4 I can’t remember if I had a period in the beginning of May since I have PCOS and didn’t track regularly. Putting all of my dates in the calculators which I don’t know if they are even accurate by ultrasounds says I conceived around mid May. I had sex April 15 & 19 with someone else due to a very bad issue and I’m hoping this pregnancy didn’t result from those two days. I’m hoping it’s my current partner which I have had sex with since those two incidents and we were together before this person in April as well. I just know implantation can take some time and just confuses me. Does anyone have advice on what they think, could it be from April?
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134578 tn?1614729226
No, not from April. I agree with the mid-May conception estimate, around the 16th-18th, since your first two ultrasounds were early in the pregnancy.

You do know, I assume, that the medical way of counting weeks of pregnancy includes the two weeks at the front end when the woman is not pregnant yet, to count in a time between the last period and ovulation? So, seven weeks "pregnant" or seven weeks "along" or "your seventh week" when said by a doctor, means five weeks since conception? "Weeks pregnant" is a bit of a misnomer that way, because it is really measuring a medically-defined pregnancy time period from the assumed first day of last period to the date of full-term delivery.

Implantation does not "take some time" -- at least, not the many weeks you are worrying about. After the fifth day from when the sperm meet the egg and creates an embryo, the embryo sheds its shell. Any time after that it can implant, and it had better, because by about the tenth to twelfth day of its existence it won't continue to exist by itself. If it has not implanted by probably the twelfth day since it was formed, the pregnancy will fail; it needs those nutrients.

Ultrasounds measure the baby (not implantation). In the fifth to seventh week (as counted by doctors, nurses, and ultrasound techs) ultrasound results are not very far off for purposes of computing when conception was, if they are off at all. (Maybe a day or two at most.) By the end of pregnancy, it's possible for an ultrasound measuring a baby to give a wrong date for conception if the baby has grown at a different rate than average. But not in your fifth or seventh week. Don't worry, you didn't conceive in April.
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Okay so the implantation can only take 12 days from the day I had sex? Because I know that sperm can last for a little in the right cervix conditions? If I remember I was bleeding around May 1st or 2nd but can’t remember exactly and I think that scared me that it was implantation after I found out I was pregnant June 10, but wouldn’t I still of showed way further on the ultrasound? Thank you for answering back such a detailed comment it really helped. Those few questions in this comment are the only ones I have left I know it’s more just me worrying but Just helping understanding if I still would’ve showed further ahead.

You look like you are trying to knock down a 'what if' scenario in which the embryo was created and then floated around for a month before implanting, and that somehow the ultrasound information indicates only when implantation was, not conception. There are a few misinterpretations in this scenario that I'll try to explain, but first I really need to say, don't let guilt or panic cause you to ignore the genuine medical information you have been given by your doctors. Not only is Dr. Internet far from infallible, but you are reading through the filters of lack of medical information and your worries, which of course will color your interpretation of what you are reading.

For example, there is a popular Internet trope, that such a thing as "implantation bleeding" exists. This idea often causes young women to write in all panicky, thinking a period probably wasn't really their period but was most certainly "implantation bleeding," and oh my god what if they are pregnant, or what if their boyfriend wasn't the dad, etc. etc. etc. If implantation bleeding exists at all (and in this community in particular, if it happened regularly we would hear about it), it would appear once, as a little tiny whiff of pink in the panties one day. An embryo is smaller than the dot on the i in this sentence, it is not going to cause someone to bleed like a period for days. From the lack of anyone ever even once writing in to say that it actually happened to them in real life, I think implantation bleeding is largely an Internet myth.

Another point, for you to know though it doesn't have much to do with your scenario -- you say "I know that sperm can last for a little in the right cervix conditions." The only thing the cervix has to do with anything is that in the middle of the month, it is more open, with mucus more hospitable to sperm. But even on an inhospitable day, it is not like the mucus will KILL sperm.

OK, about your scenario:

Once sperm is in the woman's body, it can live about 4-6 days, with some research suggesting it is no longer strong enough to penetrate the egg by day 6. For this reason it's not uncommon to see research that says sperm is only viable for 3-4 days.

There is no research I've seen suggesting an embryo can survive longer than 12 days from inception unless it has implanted, and even that research suggests if it takes that long the pregnancy probably won't succeed. Most research says an embryo can't last if it takes more than 10 days to implant. This makes sense because the embryo is ready to implant itself in the uterus once its shell comes off at day 5 or 6, and implanting will be its biological imperative because that is where the nutrition is. My doc always just said that the embryo implants on day 6, and I don't have any reason to disbelieve him from anything I've read.

But it doesn't even matter if the embryo can last 12 days or 10 or 40, or any number. Your floating-around-before-implantation scenario seems to require that the ultrasound count not begin until the embryo implants. That's not what ultrasounds do; ultrasounds know jack about when implantation was. They measure the embryo's development, and the development of an embryo begins on the day the sperm met egg. Even if a floating-a-long-time scenario were medically possible (and it isn't), the ultrasound would show a baby that began in April. Your ultrasounds showed a baby that began with sperm meeting egg in May.

Assuming your egg was fertilized within a max of 5 days after sex, and given that your two early ultrasounds indicate the baby was conceived in a time range from May 16 - 18, the sperm from the guy from the previous month was long dead, and all that 12-day stuff is unnecessary to even consider. Don't scare yourself for nothing. You're going to be a mommy, and mommies don't scare.  : ) And congrats, by the way. Many women in the Infertility community are crying for what you have. Even if you were right in your fears (and, remember, you aren't) any one of them would trade places with you in a nanosecond. You're the lucky one.

Take care,

Yes I was trying to rule out the April encounters. So just one more question and I promise I’m good and won’t bother you anymore. In order for the 19th encounter to happen I wouldve had to ovulate by the 26th of April at the latest for that to result in pregnancy which would show me much further along as you have stated correct? Especially since my first two ultrasounds were so early in the first trimester they are much more reliable correct? Even stating that my 20 week was only a few days ahead to so I should feel very confident that this was May and April was impossible to conceive this baby? Thank you for taking the time to talk to me I don’t have many people I can ask these questions and feel confident they know what they are talking about. I’ve been really hard on myself and lost a lot of happiness due to this. Talking with you made it to where I can breathe now.
The evidence of your baby's size shown on the early ultrasounds shows you ovulated in the time period between May 16 and 18. Knowing what you now know about how long sperm lives, in what scenario would the sex on the 19th of April produce the pregnancy? You said "I wouldve had to ovulate by the 26th of April" -- in fact you would have had to ovulate by the 23rd or 24th of April. (Did you? No.) And the embryo's size and developmental markers on two early ultrasounds would have to be wrong. (Were they? No.)

A doctor looking at a gestational sac and yolk sac (only) on an ultrasound would not identify it as anything else besides an embryo in the very early stages, which your doctor correctly did. The embryo was identified as being in the fifth week GA (which, you now know from what is written above, means the third week since conception).

Often doctors will give a margin for error for ultrasounds done later in the pregnancy, because babies can grow at different rates. But all embryos begin as one cell, and divide into two, then four, then 8, then 16 cells etc. at a known rate. It's not until the 12th week that a noticeable margin for error (+/- 7 days) needs to be added if trying to use an ultrasound to date a pregnancy, to account for the fact that some grow faster and others more slowly than the average. This is not an issue in the fifth week when the baby is merely a gestational sac and a yolk sac. It is too new to diverge from averages.

Please stop going 'what if, what if, what if.' All it will do is make you nuts. Stick with the real medical facts and it should calm your anxiety.
Hi Annie,

So all of your comments made me feel so much better and relieved and I understood everything you said. Until today, I went in for a growth scan I have Gestational Diabetes and I am 36 weeks well on the ultrasound today they said they are measuring my baby at 39 weeks 4 days!! When I put that in any calculator or anything it starts to line up with the dates where I was with the other person! I’m freaking out and just wanted to reach out to you to see if you could help ease my mind again or if I am screwed and this mess up will forever haunt me. I feel like a terrible person and I hate bothering you but your knowledge is very useful and helps a lot because it seems like you really know what you are talking about with this. Again, sorry to bother you.
By week 40, ultrasounds can be way, way off. I said so at the beginning, if you would read the posts again. Especially someone with GD, babies can be really big. Please remember that when your baby was in the fifth week, it looked like a yolk sac and a gestational sac, not like a baby in its ninth week.
Okay thank you that’s what I was telling myself but I did the worst and googled about accuracy and I saw some ladies saying their dating scans were off and they didn’t trust them and they think their LMP was right not the scan so I just wanted to reach out to you again because I got startled and since you have the knowledge. Sorry I really am.  Currently staying off google and trying to remember the medical facts your stated.
Doctors will say "plus or minus three weeks," if asked to use an ultrasound at the end of pregnancy to estimate the date of conception. The margin for error gets really wide. Your doc saw and measured your actual baby in its fifth week, and it looked like a baby in its fifth week.
This is correct, also my 8 week measured only 2 days difference and had a crown rump of where it should. My 20 week was even pretty close only a few days ahead and I know the error gets wider by then. Thank you again. I just have to remember these things and keep telling myself there’s no possible way April dates made this baby. It was May and I have to remember that!
Avatar universal
Agreed, May 18th was the most likely ovulation date for this pregnancy.
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