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Date of conception and due date

I was on birth control for more than 5 years.

Dec 29 I got my period and stopped on Jan 1. On Jan 2nd, I started a new pack of birth control, BUT I ONLY TOOK 5 PILLS FROM THAT PACK AND STOPPED.

Then on Jan 18, I fooled around (did NOT have intercourse at all, but he touched me and I think he might have had semen on his fingers) anyway, on Jan 28 (two days after my "expecting" period) I started bleeding and it last 3 days. Was this just a two days late period or was it implantation bleeding?

Then I had sex without protection with my boyfriend on Feb 6, 8, 10 and 11. Then I found out on Feb 28 that I was pregnant! (My period that was supposed to come on Feb 25, didn't come!)

I went to the doctor for the first time on March 07. He said the ultrasound showed nothing, just the sac, it was too early to see anything else, and that I was PROBABLY between 4 to 5 weeks, but my hcg blood levels showed that I was 5-6 weeks.

When I went back on April 11, the ultrasound showed 10w4d with CRL 3.66cm ...SO FAR MY DUE DATE IS NOV 4TH. All the ultrasounds matched up to my 21 week. My last ultrasound at 21w4d the baby was measuring 22w5d. DR STILL DID NOT CHANGE THE DUE DATE!!!

Why after 21 weeks the baby started to measure a week ahead? Which ultrasound is more accurate dating conception? When did I conceive, in Jan or Feb?

Thank you so much.


The doctor is taking your period which started on 28 January as your last period and this date is used to calculate your expected due date, along with the ultra-sound scans he has done.

If you had conceived in January, then 29 December would have been used as your last period and the ultra-sound would have showed something more significant than just the sac on 7 March. Also there would be a greater discrepancy in the size measured and the current due date, if you had conceived earlier.

Most probably, your date of conception is mid-February and so your boyfriend is the father of your baby.

Research has shown that the earlier ultra-sounds are more accurate, in terms of predicting due dates, than later ultrasounds. This is most probably why your doctor has not altered the expected due date, even though your baby is now measuring a bit bigger than average for this stage of pregnancy.

Remember, ultra-sounds are based on average sizes and every baby is different.

How big your baby will grow is mostly determined by your diet and state of health. (By the way, to ensure you have a healthy labour, make sure you eat a lot of fruit and vegetables in the next few months to build up the levels of micronutrients that your body needs to function effectively during the marathon of labour!)

Ultra-sounds in general are really not very accurate for determining due dates. A recent study has shown that birth dates and due dates may vary by as much as five weeks!

The baby determines his or her own date of birth and a due date should simply be a rough guide for you to know when to expect your baby.

So you would be wise to be ready anytime from two weeks before your due date to two weeks after. In fact, set your mind on mid-November so that if you go overdue that it will be easier to deal with mentally!

Spend these next few months considering your Birth Options as the highly medicalized way that most western women birth in hospitals is not good for mothers or for babies.

For normal healthy women, a gentle, natural approach with as little intervention as possible has lifelong benefits to the baby and to the mother-child relationship.

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