I am almost embarrassed asking this one, being that I know my share of biology, but this kinda stumps me. Keep in mind that I am not a father yet either.
So, human Woman gets inseminated, one cycle later, she misses ovulation and menstruation, finds out that she is preggers.
Is it 8 months from then until birth or 9 from that point? From the date of conception, do humans have a ten month or nine month gestational period?
It doesn’t make any difference if she never finds out until the baby pops out. The time is approximately 9 months from the time of fertilization. I believe that there are cases much longer, maybe as much as 11 months or almost that. And of course, there have been viable births after about 6 months or so. I’d search for it but it’s late.
Here’s how it works:
A woman is pregnant, usually, for 40 weeks.
When conception happens, she is already considered to be 2 weeks along. Weird, yes, considering she’s not pregnant those first 2 weeks of her cycle, but that’s how it is.
So when a woman finds out she’s pregnant (assuming she finds out when she misses that first period), she’s already considered 4 weeks gone, even though the baby has only actually existed for 2 weeks.
So, to answer your question, from the time that sperm meets egg, the kid’s in there about 38 actual weeks. If the baby manages to be born on the official due date (this happens only about 5% of the time, btw), he or she would be considered 40 weeks gestation, though, rather than 38 (the actual amount of time spent in the womb).
Then, of course, there’s exceptions. One baby I know of was born at 20 weeks. I personally didn’t show up until the 43rd week.
Another factor is cycle length. Mine is 34 days, about six days longer than most. Knowing that they add a few days to calculate the due date.
My 90-year-old great aunt told me that it is an old wives tale that it takes 9 months to have a baby. She said that is only for the second baby; the first one can come anytime. 