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how accurate are 6 week ultrasounds for establishing conception dates?
Hi,
I would really appreciate not being judged because I am already beating myself up over this. I had a period on May 10, 2021 (27 day cycles). On May 17-18, I had sex with a guy and I did take a plan B, but I took it 72 hours after which of course alters it’s effectiveness.
On 5/27, I experienced light cramping and bleeding. I went to the doctor thinking I was miscarrying and the plan B may not have worked. Or maybe I was already pregnant? I didn’t know what was going on. The bleeding was dark, had a gray large clot, and lots of tissue that looked odd to me. I took a physician administered pregnancy test and had blood work done, and it was negative.
We broke up, never had sex again, and I ended up having sex with someone else throughout the week of June 7-June 13(He did know that I had sex with someone else in May, I was not hiding this.)
Weeks later, I got really sick and couldn’t keep anything down. I go to the doctor on 7/4, and I’m pregnant. When I went in for my first ultrasound on 7/8, apparently it was too early to spot heartbeats, the sacs appeared to be empty, and babies measured at 6w3d, due date 2/28. This was a vaginal ultrasound so it was pretty early.
Using a conception calculator, I immediately thought it was guy 2 as he said he could recall when he possibly slipped up, and it matched up with the dates the conception calculator listed. I also put in the calculator that my last period was on 5/27, and the calculator gave me the same due dates doctors have given me. So I thought it was a match. The babies due date changed at my 8 week ultrasound and was put to 3/2. All of my scans have been consistent with the dates of 2/26-3/4. I get lots of ultrasounds because I’m high risk, so I’m very aware of their measurements. I realize taking a paternity test when the babies are here is the only way to 100% prove things, but would my ultrasound consistently be off, especially since I got it so early in my pregnancy? Is it possible that the bleeding on 5/27 was withdrawal bleeding and not a period? :( Any advice is appreciated. I’ve been having anxiety attacks and stressing so much because I feel so horrible. I have zero communication with guy 1, and do not really want him involved. Thanks in advance.
I would really appreciate not being judged because I am already beating myself up over this. I had a period on May 10, 2021 (27 day cycles). On May 17-18, I had sex with a guy and I did take a plan B, but I took it 72 hours after which of course alters it’s effectiveness.
On 5/27, I experienced light cramping and bleeding. I went to the doctor thinking I was miscarrying and the plan B may not have worked. Or maybe I was already pregnant? I didn’t know what was going on. The bleeding was dark, had a gray large clot, and lots of tissue that looked odd to me. I took a physician administered pregnancy test and had blood work done, and it was negative.
We broke up, never had sex again, and I ended up having sex with someone else throughout the week of June 7-June 13(He did know that I had sex with someone else in May, I was not hiding this.)
Weeks later, I got really sick and couldn’t keep anything down. I go to the doctor on 7/4, and I’m pregnant. When I went in for my first ultrasound on 7/8, apparently it was too early to spot heartbeats, the sacs appeared to be empty, and babies measured at 6w3d, due date 2/28. This was a vaginal ultrasound so it was pretty early.
Using a conception calculator, I immediately thought it was guy 2 as he said he could recall when he possibly slipped up, and it matched up with the dates the conception calculator listed. I also put in the calculator that my last period was on 5/27, and the calculator gave me the same due dates doctors have given me. So I thought it was a match. The babies due date changed at my 8 week ultrasound and was put to 3/2. All of my scans have been consistent with the dates of 2/26-3/4. I get lots of ultrasounds because I’m high risk, so I’m very aware of their measurements. I realize taking a paternity test when the babies are here is the only way to 100% prove things, but would my ultrasound consistently be off, especially since I got it so early in my pregnancy? Is it possible that the bleeding on 5/27 was withdrawal bleeding and not a period? :( Any advice is appreciated. I’ve been having anxiety attacks and stressing so much because I feel so horrible. I have zero communication with guy 1, and do not really want him involved. Thanks in advance.
COMMUNITY LEADER
You said you took a Plan B 72 hours after the sex, which "of course alters it’s effectiveness." For the sake of other readers who might use Plan B, I should note that Plan B is most effective if you take it within the first 3 days after sex, and 72 hours qualifies.
Anyway, if I'm understanding what you are worrying about, it's whether sex from May 17/18 could have produced the pregnancy. One way to think about this is to work out how far along the pregnancy would have been at different points if that earlier sex had produced it. For example, when you went for an ultrasound on July 8, the babies would have been in their eighth week, with heartbeats, waving arms and legs, and swimming around like acrobats flying in the air. But you just saw sacs. And babies look different each week, and doctors look at that. It's not like doctors would ignore it if the babies were three-plus weeks further along than the GA said. And they wouldn't have looked like sacs with no heartbeats on July 8.
You are asking whether an ultrasound in your 6th week can be used to establish a conception date, and it can. But in your case, your due date doesn't hang on just your 6th week ultrasound -- you've had a lot of ultrasounds and the doctor checks developmental markers against the GA each time. The whole string of ultrasounds would have to be wrong to back up the first being wrong, if it was. Doesn't sound like they are wrong.
Anyway, if I'm understanding what you are worrying about, it's whether sex from May 17/18 could have produced the pregnancy. One way to think about this is to work out how far along the pregnancy would have been at different points if that earlier sex had produced it. For example, when you went for an ultrasound on July 8, the babies would have been in their eighth week, with heartbeats, waving arms and legs, and swimming around like acrobats flying in the air. But you just saw sacs. And babies look different each week, and doctors look at that. It's not like doctors would ignore it if the babies were three-plus weeks further along than the GA said. And they wouldn't have looked like sacs with no heartbeats on July 8.
You are asking whether an ultrasound in your 6th week can be used to establish a conception date, and it can. But in your case, your due date doesn't hang on just your 6th week ultrasound -- you've had a lot of ultrasounds and the doctor checks developmental markers against the GA each time. The whole string of ultrasounds would have to be wrong to back up the first being wrong, if it was. Doesn't sound like they are wrong.
4 Comments
Thank you. I am honestly just worried because I’m nervous the eggs may have implanted really late and the bleeding I had on 5/27 may have not been a period and it’s driving me crazy. Or maybe that the babies just grew slow?
I got a 4d ultrasound and one of the twins looks sort of like the first guy and that also is making me second guess. There was either 20 or 21 days between the encounters which I thought would be enough to determine but I’m just not 100% sure and don’t want to be wrong.
I got a 4d ultrasound and one of the twins looks sort of like the first guy and that also is making me second guess. There was either 20 or 21 days between the encounters which I thought would be enough to determine but I’m just not 100% sure and don’t want to be wrong.
Regarding your notion that the "eggs may have implanted really late," embryos begin to develop on the day sperm meets egg, not the day they implant. (They are growing and dividing well before they implant, and just keep on doing so.) When a doctor measures the baby's growth markers and crown-to-rump measurements, he or she is not measuring the length of time since implantation. Also, an embryo needs to embed in the uterus between the sixth and tenth day of its development. If your embryos had implanted "really late," they would not have in fact been alive and wouldn't have implanted at all.
You are thinking that the babies grew so slowly that all their markers are three weeks delayed? What kind of medical evidence do you have from all the ultrasounds suggests they are that delayed?
The bleeding you had beginning on May 27 may have been prompted by taking Plan B -- basically, what prompts a period is that a woman gets a lot of progesterone, then the progesterone stops, and a period comes. That's what happens naturally (your progesterone builds up and then drops, and a period comes) and Plan B uses progesterone to do the same thing. No matter what prompted it, a period obviously did come on May 27, and according to the evidence of your ultrasounds, it acted like a period acts.
If you genuinely think there is a chance that the sex on May 17 produced the babies, seriously, how do you explain no heartbeat on July 8?
You are thinking that the babies grew so slowly that all their markers are three weeks delayed? What kind of medical evidence do you have from all the ultrasounds suggests they are that delayed?
The bleeding you had beginning on May 27 may have been prompted by taking Plan B -- basically, what prompts a period is that a woman gets a lot of progesterone, then the progesterone stops, and a period comes. That's what happens naturally (your progesterone builds up and then drops, and a period comes) and Plan B uses progesterone to do the same thing. No matter what prompted it, a period obviously did come on May 27, and according to the evidence of your ultrasounds, it acted like a period acts.
If you genuinely think there is a chance that the sex on May 17 produced the babies, seriously, how do you explain no heartbeat on July 8?
This made me feel a lot better. Thank you. I do suffer from anxiety and just started therapy to help with this because I’ve been going down a rabbit hole for almost 7 months. It’s good to hear an unbiased opinion to put things into perspective. I appreciate it
Well, as I'm sure your therapist will affirm, going down the rabbit hole never helps a thing.
OK, so now having clarified the babies' paternity, let's talk about the entirely different reason you should have a DNA test when the babies are born. To the guy, you arranging for one will be welcome. He likely doesn't want to offend you, but should be relieved at the chance to be sure you are not taking him for a ride. So offer to set it up if you haven't already, and arrange with your doctor to get a legally admissible DNA test while you are all still at the hospital with the babies. (And, go with him when he gets swabbed, and do it all together.)
Your own hidden reason is that it saves a lot of effort later if proof of the babies' paternity is in their medical record from the start. If the guy is your husband, the law assumes he is the dad (and it takes some legal footwork to refute that). But if you two aren't married, that DNA test gives your babies the legal right to support from him. If things go south between parents, trying to get DNA tests needed for child support can involve legal summonses and the like. It's far simpler to do at the beginning, which is when he's most likely to have been wondering anyway.
I wouldn't share your reason for wanting the DNA test with him, just represent that you are offering it so he will never have to wonder. (You don't want to basically point out that if he were to shirk taking the test, it's going to put the burden of proof on you later.) For the same reason, go with him (or send your best friend) to the lab when he gets swabbed. (Since the babies and you also need to be swabbed, it will be only natural to all go together and do it at once, so this shouldn't be hard.) This is because a guy who really doesn't want to be a dad might think of sending a look-alike buddy to the lab to get swabbed in his place, and tell you he went to the lab. Let's be clear that nothing you've said makes me think he's trying to get out of fatherhood, this is just about doing things in such an up-front way that there are never any questions later.
OK, so now having clarified the babies' paternity, let's talk about the entirely different reason you should have a DNA test when the babies are born. To the guy, you arranging for one will be welcome. He likely doesn't want to offend you, but should be relieved at the chance to be sure you are not taking him for a ride. So offer to set it up if you haven't already, and arrange with your doctor to get a legally admissible DNA test while you are all still at the hospital with the babies. (And, go with him when he gets swabbed, and do it all together.)
Your own hidden reason is that it saves a lot of effort later if proof of the babies' paternity is in their medical record from the start. If the guy is your husband, the law assumes he is the dad (and it takes some legal footwork to refute that). But if you two aren't married, that DNA test gives your babies the legal right to support from him. If things go south between parents, trying to get DNA tests needed for child support can involve legal summonses and the like. It's far simpler to do at the beginning, which is when he's most likely to have been wondering anyway.
I wouldn't share your reason for wanting the DNA test with him, just represent that you are offering it so he will never have to wonder. (You don't want to basically point out that if he were to shirk taking the test, it's going to put the burden of proof on you later.) For the same reason, go with him (or send your best friend) to the lab when he gets swabbed. (Since the babies and you also need to be swabbed, it will be only natural to all go together and do it at once, so this shouldn't be hard.) This is because a guy who really doesn't want to be a dad might think of sending a look-alike buddy to the lab to get swabbed in his place, and tell you he went to the lab. Let's be clear that nothing you've said makes me think he's trying to get out of fatherhood, this is just about doing things in such an up-front way that there are never any questions later.
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