So just how accurate are invasive conception tests?

May 4, 2008 8:55 AM

How possible is it to narrow down a babies date of conception to a 24 hour period after a little over a month?

BACKSTORY:
A few weeks ago, my girlfriend informed me (guy number 1) she was pregnant. Not a problem. Well, she told me that she was two months pregnant, and we'd only been dating for a month (at the same time she was dating another gentleman (guy number 2), but she was upfront about it being casual on both counts). Still, not a problem to me (what can I say, I really like her). However, she wanted to be with the father (long story, but it's not 'cuz she cares for him, it's simply because he's the father, BUT this is guy number 3). Well, now come to find out, she's only a little over a month pregnant. See, the other gentleman (guy number 2) wanted her to get some sort of invasive check done, and apperently it's been narrowed down to the friday of the weekend we first had sex. But she and I only had sex on that Sunday.

So, what I'm wondering is just how accurate are these invasive tests? Could the child be mine? Or when the doctor says (after a little over a month) that the child was concieved within 24 hours of the friday in question, they're pretty much spot on?

And please, I know how stuipd I am to have gotten into a relationship like this. Trust me, it makes only margenally more sense from the inside. However, please no comments on that. Just on the whole baby thing.

posted by TrueVox to health (50 comments total)

What was the test? If it was an ultrasound they are reasonably accurate but I wouldn't think ~that~ accurate.
posted by fshgrl at 9:06 AM on May 4

The ultrasound that my wife had narrowed the date of conception to right in the middle of a week I was across the country for work. We figure we know when the little guy was conceived, and it was probably the weekend before, so from this sample of one, you get +/- 4 days.
posted by chookibing at 9:11 AM on May 4 [1 favorite]

I don't know what it was. :( I'll ask though. But, an ultrasound wouldn't be considered "invasive", would it? Because she specifically used the term invasive.
posted by TrueVox at 9:16 AM on May 4

An ultrasound this early would be transvaginal (aka "dildocam").
posted by peep at 9:21 AM on May 4

Wow. That... that is the greatest word ever.

So, THAT might be considered Invasive, right?
posted by TrueVox at 9:22 AM on May 4

Unless a woman has had IVF, it is not really possible to pinpoint conception with that much accuracy.

I want to stress that dildocam is, uh, NOT a medical term. But here's a picture (SFW).
posted by peep at 9:27 AM on May 4

This site on paternity testing says that an ultrasound can only be accurate to 5-7 days in the first trimester.
posted by saffry at 9:30 AM on May 4

Ultrasound dating of conception is not reliable for determining paternity because the ultrasound can be off by at least 5-7 days in early pregnancy.

Being a cynic, my first question would be was the doctor that specific, or did your girlfriend infer the Friday from his range. "So that would tie up with my Saturday intercourse with my boyfriend, yeah?"

On an unrelated note- unprotected sex with three guys in two months. Impressively stupid.
posted by Static Vagabond at 9:39 AM on May 4

Should have previewed, saffry got in there first (h/t)
posted by Static Vagabond at 9:42 AM on May 4

not to be snarky, but this alone makes using a condom worthwhile.

the child COULD be yours, but whether it is....you'll need a dna test. you can do these in utero if your really have to, but i think it's a bit safer for the baby after it's born.
posted by thinkingwoman at 9:42 AM on May 4

Yeah, like I said, Static. There's a lot of stupid involved in this, but that's not what I'm asking about (though you ARE correct).

And thank you all for your answers. But what's an IFV? Are you refering to Invitro Fertilization? Or is there something else?

Also, are we fairly certen that the, uh, dildocam is the most likely thing done? Are there any other things it could be?
posted by TrueVox at 9:43 AM on May 4

IVF yeah, invitro-- it obviously doesn't apply to you, in that case they could just look at the chart... :)

Only way for actual proof wait until 6 or 7 weeks into the pregnancy and get a DNA test done. I can't imagine for a moment the accuracy of conception date would get any easier as the fetus increased in size.

I hope it works out well for you TrueVox.
posted by Static Vagabond at 9:55 AM on May 4

Why don't you ask your girlfriend what was done?

If it is because you don't trust her to tell the truth about it, why do you trust that the reported conception date is accurate?

There is all kinds of bad in this situation; you don't have enough information to figure out the answer you're looking for and the tests aren't accurate enough anyway. It sounds to me like she is deciding who she wants the father to be and making the facts fit that decision.

IFV is indeed in vitro fertilization. If you have a doctor perform IFV, you know exactly when conception occurred. Failing that we return to the idea that she is just deciding who she wants the father to be and presenting "facts" to back that up.
posted by Justinian at 9:55 AM on May 4

I think the girl might be making things up to make the scenario fit whomever it is she wants to be the father. Invasive test? What invasive test? Wait for DNA.
posted by astruc at 9:56 AM on May 4 [2 favorites]

Yes, IVF is in-vitro fertilization. No, you can't pinpoint conception date that carefully this early.

And, sorry to suggest this, but: please go get yourself tested, right now, for gonorrhea, chlamydia, and syphilis. In 2-3 months, follow up with an HIV test. You've been having unsafe sex with a girl who has been having unsafe sex with at least two other men that you know of. She should get checked out too--you both need to make sure you haven't taken on any other passengers.

Also, buy and use condoms.
posted by dirtynumbangelboy at 9:58 AM on May 4 [2 favorites]

The only way to be 100% sure this baby is yours is a DNA test. Do not rely on any other test to tell you when the baby was possibly conceived. Even if there was a test that could narrow it down to a 48 hour window, how can you be sure she was only with you during that time? And from the sounds of things, you can't really rely on much of anything she's telling you especially with 3 (that you know of) men involved. A DNA test will give you a definitive answer so there will not be any wondering or guessing. Until you get the results from a DNA test (and actually see them yourself), take everything she says with a grain of salt.
posted by GlowWyrm at 10:11 AM on May 4

Sounds like you'll need a DNA test to be sure, especially since it sounds like none of you are super eager to claim the pregnancy as yours. That will probably have to wait until the baby is born because it can be risky for the pregnancy to do it in utero.
posted by fructose at 10:14 AM on May 4

Ha! I love the link!

OK, as far as the condom comments.... you're all right. But that's not at all what I was asking about. To be honest, we did use 'em. Used one the first night, but it came off in the heat of passion. I used one every other time.

Getting tested? Not a poor idea. Likely will. But not what this question was about.

Also, I just spoke with her, and she doesn't remember the name of the procedure. She mentioned that they checked her cervix and a few other things... I hate to say it, but I think you may be right, that she may just be giving me a line to fit what she wants. :(
posted by TrueVox at 10:18 AM on May 4

Oh, and to Fructose, actually I'd be fine if it was my baby. If I didn't want it, I'd just let her go with what she's saying (which is that it's guy #2's).
posted by TrueVox at 10:20 AM on May 4

Getting to the technical end, a woman isn't fertile for that many days each month. The actual conception (sperm 'n' egg meet) doesn't happen til later.
At the ultrasound they measure the baby and based on that (and reported sexual activity) they estimate conception date.

But there is NO WAY that the doctor said 'yup. it was Friday the 10th.'

Wait for the DNA tests or have her chart out her sex life and periods. Assuming she was fertile during days 10-20 after her period was done, any sperminators in that time are more likely. But for reals, wait on the DNA test.
posted by k8t at 10:22 AM on May 4

I don't know what state you're in, but you don't want to serve as the dad only to find out years later that it's not yours and have your rights possibly compromised if the bio dad (if it's not yours) decides to pursue a relationship with the kid. That's why a test initially is a good idea.
posted by fructose at 10:27 AM on May 4

Sounds like she got a pap smear which is normal for 1st month appointment. It is 'invasive' as they widen the cervix and scrape some cells out.
This would not result in any information about conception.
But in that first visit the doctor would try to determine conception date.
posted by k8t at 10:29 AM on May 4

Even if the woman in question could absolutely pinpoint the day that she ovulated, with the factors involved here, it's still too hard to determine who provided the sperm. Sperm can live for something like 5 days under fertile conditions inside the woman. So hypothetically, she could have sex on Friday, Feb 1 with Guy A, then ovulate on Monday, Feb 4 with Guy A sperm merging with egg that day. But if she also had sex with Guys B and C on Saturday and Sunday, any one of those sperm might have been the victor too. The ultrasound would basically be able to agree that the fetus was conceived around the Feb 4 date as opposed to two weeks earlier or later, but it can't tell you whose lucky sperm hit that egg the day she ovulated.
posted by xo at 10:35 AM on May 4

Xo, could it tell if she ovulated on the Friday? Is that what she may be referring to?

And I'll have to ask if it was a Papsmear... if I even want to persue this further. It seems (according to your folks comments) that she's making stuff up to place her with her current guy, so I donno if I even want to mess with that. I've already been through a relationship that ended with me not seeing much of my son... donno if I want a repeat. If there was decent chance of us ending up together, then yes, I'd be quite happy... but another thing like my last one would be horrable...

So... thanks, all. i guess I have what I need. Mostly. I think? :)
posted by TrueVox at 10:43 AM on May 4

TrueVox, no, they can't tell that closely. Even if she didn't have sex for a year, then had sex with two different guys, one on Friday and the other a week later on Friday, based on the size of the fetus it'll be too close to call. And they still wouldn't know if it was Guy A's sperm lasting 5 days to catch the egg, or Guy B's sperm freshly catching the egg the minute it was released.
posted by xo at 10:54 AM on May 4

OK, then she's just made up her mind, and is working with it. Thanks a lot, gang. Not neccessarly the answer I WANTED, but it's the accurate one, and that's what I NEEDED. :)
posted by TrueVox at 10:58 AM on May 4

[a few comments removed - question is specific you can answer "unsked questions" in mefimail]
posted by jessamyn at 11:32 AM on May 4

I think the girl might be making things up to make the scenario fit whomever it is she wants to be the father.

Just want to point out that it's very possible for her to do this without even being conscious that she's doing it. Extreme circumstances bring out interesting psychology in everyone they touch.
posted by [NOT HERMITOSIS-IST] at 11:34 AM on May 4 [1 favorite]

Also, even if she's just trying to brush you off, you need to have this settled officially because if that other guy winds up brushing her off, guess who she can try to come after for child support?
posted by [NOT HERMITOSIS-IST] at 11:36 AM on May 4

Yep, this can only to determined by a DNA test. Whether or not you are the father, you need to be sure either way, given the 18 years of child support that are at stake.

And this should go without saying, but in case not: make sure YOU actively take part in the DNA test (i.e., you show up for them to swab your saliva, or whatever), and YOU actually see the results. Do not rely on her on either score.
posted by scody at 11:55 AM on May 4 [1 favorite]

[gah, "to" = "be." No caffeine yet.]
posted by scody at 11:56 AM on May 4

TrueVox you're very quickly descending into a realm of legal peril. You should talk to a lawyer about the applicable paternity laws in your state and be prepared to act.

A paternity test in this case is a double edged sword. It could get you off the hook. It could also sucker you with 18-years of child support payments. Best case scenario: she settles down with one of the other guys, his name is put on the birth certificate, no DNA test is conducted, and you walk away from this mess a little wiser.

Don't let yourself be taken advantage of! Talk to a lawyer right now.
posted by wfrgms at 11:58 AM on May 4

um... do you actually have any proof that's she's pregnant? all the very vague details lead me to doubt the original premise. still a good idea to get tested, you and her and whomever, for everything and anything, though.
posted by mr_book at 2:09 PM on May 4 [1 favorite]

Speaking from personal experience, with my second child, I knew I was pregnant before I had even missed a cycle. I went to the doctor over a week later, and they were only able to tell I was pregnant through a blood test, because (and at this point I was 5 weeks pregnant) it was impossible to tell by an invasive physical exam at such an early stage. The doc even said, "Are you sure you are pregnant?" and since I was, it wasn't an issue to me, but the point is, if she is less than 5 1/2 weeks pregnant, it would be difficult even to verify a pregnancy, and certainly the date of conception would be impossible to pinpoint with 24-hour validity.

Now, to go with more than just anecdotal evidence, "It is possible to detect a pregnancy of 5 ½ weeks gestation on ultrasound. A tiny sac can be seen, but the baby and their heart beat may not be detected yet. Be aware that while it is possible to see a pregnancy this small, in many cases the pregnancy may not be detected, because the sac is so tiny." via

You sound like a decent guy caught in a sticky situation, and she sounds like a scared young woman trying to make things work out the way she wants them to. Since legal and practical issues like childcare and child support are involved, consider doing the DNA testing ASAP if you think you could be the father. Good luck.
posted by misha at 2:27 PM on May 4

Doing a DNA test on a fetus does carry some risks. If there is no other reason for doing one, the doctor may recommend waiting until the baby is born. So be prepared for the possibility that you may have to put up with the uncertainty for another 8 months.
posted by metahawk at 3:10 PM on May 4

I know this is a quasi-medical question, but you also need to get legal advice. As others have pointed out, you could be hoodwinked into hundreds of thousands of dollars of support and college tuition (courts are increasingly required support through college years). On the other hand, you could get cheated out of a relationship with your son or daughter. If you think you are the father and want to be active in the child's life, you'll probably need to register yourself so it can't be adopted out without your knowledge. It's a bad situation and it's easy to get screwed, no matter what your preferences are. If you are a student, see if your institution has a legal services office. Otherwise, fork over the money and see a lawyer. It will be worth it.
posted by the christopher hundreds at 3:25 PM on May 4

No, she's defenatly pregnant. She was starting to show as of last weekend...

Is that usual after only a little over a month? She's not a big girl, but she's no skinny-minni either.
posted by TrueVox at 6:33 PM on May 4

She was starting to show as of last weekend... Is that usual after only a little over a month?

If you mean her belly is starting to swell, no, that's not usual at one month. It's not unheard of, but it's more typical to start showing around 12 weeks (though of course every woman's different -- some show a little earlier than that, others don't show till much later). But 4-5 weeks is extremely early to show.
posted by scody at 7:04 PM on May 4

Wait, what? It's way too early for her to be showing. Besides, the first sign of pregnancy is almost always a woman's boobs getting bigger (painfully swollen), not her stomach getting bigger. That takes months, although it does show quicker if it's not your first pregnancy or if you're super-skinny.

You know, this whole story is starting to sound really weird. This girl does not sound very stable; first she's trying to make dates fit so that the conception date is so late that it could be yours or some other guy's, and yet she's obviously much further along and thus the conception date must have been much earlier...? I have to be honest here, you should stay away from her. You don't want to get mixed up in that kind of crazy.
posted by Asparagirl at 10:40 PM on May 4

After 1 month she is showing? That is odd, unless it is twins MAYBE.
posted by k8t at 10:43 PM on May 4

No, she's defenatly pregnant. She was starting to show as of last weekend...


No, dude. No.

You are in the unpleasant situation of being woefully uneducated about pregnancy and conception, and probably being played by either an ignorant or wishful girlfriend.

A woman's menstrual cycle ranges from 24 - 35 days, with 28 being the text book example but by no means a standard. Two weeks before menstruation, a woman will ovulate. Generally, she has a 24 hour window in which to conceive, but as has been pointed out, under ideal conditions sperm can (but rarely do) survive for up to 5 days. These would have to be the five days before ovulation, though.

Ovulation in young women is, by the way, notoriously unpredictable. In addition, most women are unaware of when they ovulate. Accurately predicting this date requires temperature taking and checking cervical mucous. So don't let her tell you she knows when she got pregnant; she doesn't.

Failure to get pregnant during ovulation is what triggers menstruation; success in getting pregnant is what triggers babies. However, with either an abdominal or trans-vaginal utrasound, it is not possible to definitively date a pregnancy in the first trimester. There is at least a 7 day margin of error.

A pregnancy cannot be dated to anything closer than a one week range in the first trimester - not with a blood test or with either kind of ultrasound. She doesn't know how pregnant she is; she has a physician's best guess. It is only a guess.

She is not showing. Most women in a first pregnancy don't start showing until 15 or 17 weeks. At this moment in the fetal development timeline, we're talking about something the size of a kidney bean. There is nothing to show, although progesterone can cause bloating.

Paternity testing is your only option here. It can be done later during the pregnancy, but be aware that it carries a not insignificant risk of miscarriage. It can be done far more easily, with no risk and for less money with mouth swabs immediately after birth.

Either way, that link gives you some good information about why accurate paternity is critical. Don't be baby blind; get tested at birth.
posted by DarlingBri at 10:45 PM on May 4 [3 favorites]

All the estimates for my wife's current pregnancy put the date of conception about two days ahead of when it actually was (when you're married and have a three-year-old you know damn well when you sex).
posted by sycophant at 3:20 AM on May 5

Both of my ivf pregnancies have not been able to be dated that specifically!
It's just not possible. Even when you know when conception happened because it was done in a petri dish.

Vaginal ultrasounds are frequently done really early... i.e. before 12 weeks.
Some women might consider them to be invasive. After a pap smear, I consider them a walk in the park... so to speak.

Good luck with all of this.
posted by taff at 3:50 AM on May 5

Oh, and she might be "showing" because she's got crampy windy farty stuff happening. My pregnancy book says this is common.... ("What to Expect When You're Expecting").
posted by taff at 3:58 AM on May 5

So, probley a little late to ask this, but are any of you who've answered someone with a medical background? Just curious, but either way, I am really thankful for everyone's input.
posted by TrueVox at 4:46 AM on May 5

I have a medical background, I've given birth, I've assisted many, many women thru pregnancy and childbirth, and I echo... pretty much everything that's been said.
posted by houseofdanie at 9:45 AM on May 5

I have a medical background, I used to spend a considerable part of my life talking to teenagers who thought they were pregnant and explaining the mechanics of ovulation and conception, I am a veteran of infertility, and I have spent more time with the dildocam than with my husband. I promise you that I really, truly know what I'm talking about here. As do most people in this thread. It isn't mysterious; it's science.

A bit of internet research will back up anything I've said, but you might also want to talk to someone at your local Planned Parenthood if you want to go over this in person. Otherwise, send me a MeMail and I'll be happy to get out a calendar to plot your timeline and phone you if you like. You're in a tight spot and I'm sorry you're there.
posted by DarlingBri at 3:50 PM on May 5

Oh, no! It's not that I doubted anyone... it's just easier to put to her if I can say "Well, I've been talking to medical people (Dr's., Nurses, etc)" rather then "Well, I've talked to folks on the Internet"... ;)

And thank you VERY much for the kind offer, Darling. I may just take you up on that, depending on how things work out over the next week or two.
posted by TrueVox at 5:13 PM on May 5

No worries, the offer is always open if you need someone to talk to, however this works out for you.

I would suggest your new mantra be "trust, but verify." Take care of yourself before anyone else, because nobody else in this situation is going to look after you, okay?
posted by DarlingBri at 5:28 PM on May 5

Thank you very much. I can't quite voice how much I appreciate that. :)


And to the rest of you, a hearty thank you as well. You've all been such a help and comfort to me. :)
posted by TrueVox at 7:51 PM on May 5