Get your Health question answered in 3 easy steps
A Doctor will be with you shortly
Ask a Doctor Now
184 Doctors are Online

Had protected sex and took ipill followed by withdrawal bleeding and had sex with other. Pregnant. Paternity?

Mar 2013
User rating for this question
Answered by
Practicing since : 1998
Answered : 5625 Questions
Can an early ultrasound be off a month in the first trimester? If I slept with someone on XXXXXXX 18 (used condom & plan b 50 hrs later) & then had withdrawal bleeding from getting off birth control on Feb 5-8 and then slept with someone else the remainder of Feb. and all ultrasounds (7,11,14,19,21,26 weeks) give EDD 11/12, would it be possible I conceived from XXXXXXX 18 encounter?
Posted Thu, 26 Sep 2013 in Sexually Transmitted Diseases
Answered by Dr. Aarti Abraham 35 minutes later
Brief Answer:

Detailed Answer:
Thanks for writing to us.
Going by your EDD, you definitely conceived in February AFTER the bleeding on the 5th of February.
First trimester ultrasounds are accurate in dating upto 3 - 5 days, so the odds of conception from the January 18 encounter are LOW, next to nil.
Of course, lots of factors like expertise of the scanner, the credibility of the centre etc, all matter, but if you had a transvaginal ultrasound scan at 7 weeks at a good centre giving you this EDD, and all subsequent scans confirming this growth, then rest, assured, you DID not conceive from the January 18 encounter.
All the best.
Above answer was peer-reviewed by
Follow-up: Had protected sex and took ipill followed by withdrawal bleeding and had sex with other. Pregnant. Paternity? 3 hours later
Thank you so much. I have been worried about this all pregnancy. My 7 week scan was done abdominally and dated me 7 wks due 11/18. Because it was preformed abdominally I have question its accuracy. I did however have another first tri ultrasound at 11 weeks that dated me with an EDD 11/12, and all of my other ultrasounds (14, 19, 21, & 27) have said the exact same date. All of my ultrasounds have either been at my doctors office, the diagnostic center at the hospital, or an outpatient diagnostic center, and all have been by different techs. Are these ultrasounds enough to conclude that they are accurate and XXXXXXX 18 is out of question? Wouldn't it be impossible for all of my ultrasounds to be off by a month? Thank you for your quick reply.
Answered by Dr. Aarti Abraham 3 hours later
Brief Answer:

Detailed Answer:
Yes, an abdominal scan is less accurate than a vaginal one, but that is only for the first trimester.
Since ALL your ultrasounds have concurred, the chances of an error are miniscule.
It is IMPOSSIBLE for all your ultrasounds to be off by a month.
In the rare event ( hypothetical ) that you conceived on January 18th .. the embryo somehow made it through the withdrawal bleed ( condom plus Plan B plus birth control ) .. and then the inaccurate abdominal scan dated it incorrectly ( smaller than it was ) - then the subsequent scans would have definitely picked up the correct gestational age.
I think you are worrying unnecessarily.
There is no chance of so many scans being off the XXXXXXX
Of course, nobody would be able to stamp it as 100 %, only a DNA paternity test would establish it beyond any doubt.
However, I do not think you need to go that far, as the chances are nil for you to have conceived on January 18th.
take care.
Above answer was peer-reviewed by
Follow-up: Had protected sex and took ipill followed by withdrawal bleeding and had sex with other. Pregnant. Paternity? 2 days later
Since my last question I have been admitted to the hospital having preterm contractions. I am dialted to a 1. I fell down the stairs last week & they are thinking this might be the cause. Contractions were hard to stop, but have slowed after multiple hours & attempts. Went for an ultrasound & she was already measuring 3lbs 10oz with an EDD 11/8! Now I am concerned about the paternity issue all over again. I know 3rd trimester ultrasounds can be off, but her weight seems big. Is there any validity in this? Change your opinion at all? I am just so stressed with all this happening. Could it actually not be preterm labor & mean I am actually further along (34 near 35 weeks)?
Answered by Dr. Aarti Abraham 5 hours later
Brief Answer:

Detailed Answer:
Hi again
A difference of 3 days is QUITE normal in the third trimester.
Please do not worry, and yes, third trimester ultrasounds are way off the XXXXXXX for estimating EDD, as compared to first trimester scans.
I can understand your predicament, as you only needed this scare of ( ? ) preterm labour to confuse you totally.
Even now, the possibility of conception from January 18th encounter seems least likely.
Even if you WERE 34 weeks ( and the fetal weight would be much more than this at 34 weeks ) you still ARE having preterm labour , a really bad coincidence !
I would reiterate that this worrying and stressing out over the paternity issue itself, could be causative, as stress is a major culprit for preterm labour.
A DNA test would conclusively close this matter for you.
All the best.
Please stop worrying about it, or get the test done which will itself stem the worry.
Above answer was peer-reviewed by
Follow-up: Had protected sex and took ipill followed by withdrawal bleeding and had sex with other. Pregnant. Paternity? 1 hour later
Thank you for your reply. DNA test is not really a possibility, probably why I am stressing so much. So either way I would be in preterm labor. Is 3lbs 10oz huge for 30 weeks? Seems large to me. I am 5'3 110 prebaby & partner is 6'2 190. You are right the stress of all of this is probably causing this. I will just try to relax. If cervix is already softening (just a little), I am dilated to a 1, and contracting is there a chance I could still make it to term? Again none of this information changes our view of when I conceived? I really appreciate you being patient with me. I have also discussed this issue with my OB & she, like you, said XXXXXXX conception isn't possible. However she isn't the one at the hospital, so since I can't talk to her for reassurance it's hard.
Answered by Dr. Aarti Abraham 9 minutes later
Brief Answer:
Average fetal weight at 30 weeks is 3lb 7 oz

Detailed Answer:


At 30 weeks, average fetal weight is 3lb 7 oz, ( + / - 7 oz ) so the current baby weight is NOT AT ALL huge.

It falls in the absolutely normal range.

It only supports the theory that you conceived after Feb 5th.

Please do not mind asking me questions, I am here to answer them :)
Yes, with proper tocolytic drugs ( drugs to relax the uterus ) you might still make it to term, as long as the contractions abate.

For the rest of the pregnancy, you would have to rest, avoid stress ( particularly on this topic ) , coitus and travelling or prolonged working hours.
I wish you all the luck.

Please forget about the January 18th episode, put it behind you, and move on to a great phase of motherhood ahead,

take care.
Above answer was peer-reviewed by
Follow-up: Had protected sex and took ipill followed by withdrawal bleeding and had sex with other. Pregnant. Paternity? 2 hours later
Well that makes me feel better. What would be the average fetal weight for a 34 weeker? The ultrasound tech also commented on the baby having hair. Is that normal? I really appreciate your unbiased answers. I know logically that XXXXXXX 18 is too far off for conception, I guess I just feel like I should be punished, thus contributing to the guilt. And sometimes I have trouble trusting science or things that are unseen/changing. My family would be mortified & I would lose/hurt beyond belief the person I love. Thanks again.
Answered by Dr. Aarti Abraham 8 hours later
Brief Answer:

Detailed Answer:
Average fetal weight at 34 weeks would be around 5 lb 3 oz.
So are NOT 34 weeks :)
Soft fine lanugo hair develops as early as 14 weeks, and proper scalp hair can be seen as early as 30 weeks, so again, no cause for worry !
Thanks for your appreciation, and I am glad for your trust in me.
You have already worried yourself sick over this, and your remorse is more than enough punishment.
How long would you let a stray event cloud over the most happy period of your life - this wonderful pregnancy and the impending more wondrous phase of motherhood ?
Again put it behind you , and trust science which to some extent, does answer our basic questions ?
The baby growth corresponding to 30 weeks is a TANGIBLE proof, not something that you cannot see, measure, or quantify objectively.
Hence, please proceed ahead without any negativity in your mind and heart.
Wish you good luck always, and am always there to answer any other doubts that would trouble you in future too.
Take care.
Above answer was peer-reviewed by
Share on Facebook
Share on Twitter
Share on Google+
Question is related to
Diseases and Conditions

The user accepted the expert's answer

Ask a Sexual Diseases

© Ebix, Inc. All Rights Reserved.
All the information, content and live chat provided on the site is intended to be for informational purposes only, and not a substitute for professional or medical advice. You should always speak with your doctor before you follow anything that you read on this website. Any health question asked on this site will be visible to the people who browse this site. Hence, the user assumes the responsibility not to divulge any personally identifiable information in the question. Use of this site is subject to our Terms & Conditions
Already Rated.
Your rating:

Ask a Doctor