Why do we calculate the length of a pregnancy from the first day of a women’s last period?
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It’s the only thing that we’ve been able to know with some degree of accuracy. Ovulation timeframes vary and sperm can live for days making the date of fertilization and implantation uncertain.
Because bleeding out of your genitals is a date that people remember and can easily track.
And in the years prior to ultrasound and blood tests it was the only method we had to date a pregnancy so it is the standard around which medical literature coalesced.
To be clear, the period date is not perfectly temporally offset from viable conception (ie. Women have different length cycles so the blastocyst can implant in the uterine wall a varying number of days after the period) but **it is accurate to within a few days in most cases, which is sufficient to provide good prenatal care.**
That said, in advanced healthcare systems you will get early ultrasounds that measure the foetus and from that we backdate a conception date and equivalent “day of last period”. And these are the dates that will go in the medical record.
In short, **first day of last period is a historical medical artefact that continues through cultural inertia and nowadays we use tests and imaging to backcalculate a “day of last period” that matches your conception day (for a normal cycle).**
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Because bleeding out of your genitals is a date that people remember and can easily track.
And in the years prior to ultrasound and blood tests it was the only method we had to date a pregnancy so it is the standard around which medical literature coalesced.
To be clear, the period date is not perfectly temporally offset from viable conception (ie. Women have different length cycles so the blastocyst can implant in the uterine wall a varying number of days after the period) but **it is accurate to within a few days in most cases, which is sufficient to provide good prenatal care.**
That said, in advanced healthcare systems you will get early ultrasounds that measure the foetus and from that we backdate a conception date and equivalent “day of last period”. And these are the dates that will go in the medical record.
In short, **first day of last period is a historical medical artefact that continues through cultural inertia and nowadays we use tests and imaging to backcalculate a “day of last period” that matches your conception day (for a normal cycle).**
Because bleeding out of your genitals is a date that people remember and can easily track.
And in the years prior to ultrasound and blood tests it was the only method we had to date a pregnancy so it is the standard around which medical literature coalesced.
To be clear, the period date is not perfectly temporally offset from viable conception (ie. Women have different length cycles so the blastocyst can implant in the uterine wall a varying number of days after the period) but **it is accurate to within a few days in most cases, which is sufficient to provide good prenatal care.**
That said, in advanced healthcare systems you will get early ultrasounds that measure the foetus and from that we backdate a conception date and equivalent “day of last period”. And these are the dates that will go in the medical record.
In short, **first day of last period is a historical medical artefact that continues through cultural inertia and nowadays we use tests and imaging to backcalculate a “day of last period” that matches your conception day (for a normal cycle).**
On average, a woman’s body works on a 28 day cycle. That means that she usually ovulates on day 14, or about halfway through.
Ovulation is when the ovum, or egg, is released from the ovary, a little organ that keeps the eggs, kind of like a bag. A woman has two of these little bags, and they generally take turns spitting out eggs.
The first day of the period is day 1, which is when the uterus, or where the baby is kept, cleans itself out to get ready for a new baby. It builds a cushion all along the inside walls to hold the baby. Then, doctors can usually guess the egg is ready to be fertilized 14 days after that. Fertilization when one sperm from the man finds its way to the egg and manages to join with it. Then a baby begins to grow.
This means the doctor counts about 40 weeks from day 1 for accurate timing, though babies are technically not in there for those first two weeks or so. If a woman was able to feel it when she ovulates, she still wouldn’t know the moment fertilization would occur because there are loads of variables (things that can affect it) to consider.
People say a baby grows for 9 months, but 40 weeks sounds more like 10 months, when in reality it’s about 9.5 months.
Women get an ultrasound, like an x-ray of the baby on the inside, and when the doctors measure the size of the baby they can give a more accurate date, still with an extra 2 weeks added because that’s the standard of measurement that’s used worldwide.
Babies actually come whenever they darnwell please.
On average, a woman’s body works on a 28 day cycle. That means that she usually ovulates on day 14, or about halfway through.
Ovulation is when the ovum, or egg, is released from the ovary, a little organ that keeps the eggs, kind of like a bag. A woman has two of these little bags, and they generally take turns spitting out eggs.
The first day of the period is day 1, which is when the uterus, or where the baby is kept, cleans itself out to get ready for a new baby. It builds a cushion all along the inside walls to hold the baby. Then, doctors can usually guess the egg is ready to be fertilized 14 days after that. Fertilization when one sperm from the man finds its way to the egg and manages to join with it. Then a baby begins to grow.
This means the doctor counts about 40 weeks from day 1 for accurate timing, though babies are technically not in there for those first two weeks or so. If a woman was able to feel it when she ovulates, she still wouldn’t know the moment fertilization would occur because there are loads of variables (things that can affect it) to consider.
People say a baby grows for 9 months, but 40 weeks sounds more like 10 months, when in reality it’s about 9.5 months.
Women get an ultrasound, like an x-ray of the baby on the inside, and when the doctors measure the size of the baby they can give a more accurate date, still with an extra 2 weeks added because that’s the standard of measurement that’s used worldwide.
Babies actually come whenever they darnwell please.
On average, a woman’s body works on a 28 day cycle. That means that she usually ovulates on day 14, or about halfway through.
Ovulation is when the ovum, or egg, is released from the ovary, a little organ that keeps the eggs, kind of like a bag. A woman has two of these little bags, and they generally take turns spitting out eggs.
The first day of the period is day 1, which is when the uterus, or where the baby is kept, cleans itself out to get ready for a new baby. It builds a cushion all along the inside walls to hold the baby. Then, doctors can usually guess the egg is ready to be fertilized 14 days after that. Fertilization when one sperm from the man finds its way to the egg and manages to join with it. Then a baby begins to grow.
This means the doctor counts about 40 weeks from day 1 for accurate timing, though babies are technically not in there for those first two weeks or so. If a woman was able to feel it when she ovulates, she still wouldn’t know the moment fertilization would occur because there are loads of variables (things that can affect it) to consider.
People say a baby grows for 9 months, but 40 weeks sounds more like 10 months, when in reality it’s about 9.5 months.
Women get an ultrasound, like an x-ray of the baby on the inside, and when the doctors measure the size of the baby they can give a more accurate date, still with an extra 2 weeks added because that’s the standard of measurement that’s used worldwide.
Babies actually come whenever they darnwell please.
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