Why do we calculate the length of a pregnancy from the first day of a women’s last period?
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wait, i have a question if anyone can answer it; what if you have a VERY irregular period? how do you calculate that 😭
wait, i have a question if anyone can answer it; what if you have a VERY irregular period? how do you calculate that 😭
It’s the most consistent measure for the general population.
Ovulation usually occurs about 14 days after the first day of the period. Some women have irregular cycles or anovulatory cycles where they don’t release an egg at all, so relying on an ovulation date is not realistic except for in rare cases where hormones or basal body temperature is closely monitored.
Additionally, sperm can live in the vagina/uterus for 5-7 days, so even if there was a one-off event where the day of intercourse is definitely known for that pregnancy, that day is not necessarily the date of conception.
The best way to get a consistent expected delivery date is the first day of the last menstrual period, so that’s the dating system we use. Even if the due date is established by first trimester ultrasound, the weeks of gestational age are still assigned by convention with day 1 being the first day of LMP.
>Why do we calculate the length of a pregnancy from the first day of a ~~women’s~~ last period
*woman’s
One woman, many women
Because it’s easier to track when you get pregnant. Imagine a couple having an active sexual life and guessing when you got fecundated, it’s easier and lots of woman do track their periods so thats why.
It’s easier because in 12 days occurs ovulation.
It’s the most consistent measure for the general population.
Ovulation usually occurs about 14 days after the first day of the period. Some women have irregular cycles or anovulatory cycles where they don’t release an egg at all, so relying on an ovulation date is not realistic except for in rare cases where hormones or basal body temperature is closely monitored.
Additionally, sperm can live in the vagina/uterus for 5-7 days, so even if there was a one-off event where the day of intercourse is definitely known for that pregnancy, that day is not necessarily the date of conception.
The best way to get a consistent expected delivery date is the first day of the last menstrual period, so that’s the dating system we use. Even if the due date is established by first trimester ultrasound, the weeks of gestational age are still assigned by convention with day 1 being the first day of LMP.
It’s the most consistent measure for the general population.
Ovulation usually occurs about 14 days after the first day of the period. Some women have irregular cycles or anovulatory cycles where they don’t release an egg at all, so relying on an ovulation date is not realistic except for in rare cases where hormones or basal body temperature is closely monitored.
Additionally, sperm can live in the vagina/uterus for 5-7 days, so even if there was a one-off event where the day of intercourse is definitely known for that pregnancy, that day is not necessarily the date of conception.
The best way to get a consistent expected delivery date is the first day of the last menstrual period, so that’s the dating system we use. Even if the due date is established by first trimester ultrasound, the weeks of gestational age are still assigned by convention with day 1 being the first day of LMP.
>Why do we calculate the length of a pregnancy from the first day of a ~~women’s~~ last period
*woman’s
One woman, many women
Because it’s easier to track when you get pregnant. Imagine a couple having an active sexual life and guessing when you got fecundated, it’s easier and lots of woman do track their periods so thats why.
It’s easier because in 12 days occurs ovulation.
We really don’t. It is a starting rough estimate. On your first ultrasound they measure multiple parts of the fetus and give a more accurate estimate of your term. after the second visit the current length of pregnancy and due date is basically solidified unless something changes throughout the pregnancy. currently going through this process with my wife. So far developmentally it is spot on accurate.
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