If you were having regular periods before pregnancy, your doctor will calculate your due date based off of your last menstrual period. This goes back to the fact that in order to get pregnant, your body ovulated—or released an egg—roughly in the middle of your cycle and it was fertilized by sperm.
Knowing when your last period was can give your gynecologist (or nurse practitioner) a lot of information. For example, it can help pinpoint where you are in your menstrual cycle, which can affect your vaginal discharge, your breast exam, and things like bloating and cramps.
This is because pregnancy is counted from the first day of the woman's last period, not the date of conception which generally occurs 2 weeks later, followed by 5 to 7 days before it settles in the uterus.
If you don't know the date of your last period or when you conceived, talk to your provider. They will do an exam, which will likely include a prenatal ultrasound, to determine how far along you are in your pregnancy.
Ultrasound: At some point during your pregnancy, you will likely have an ultrasound scan. This enables your healthcare provider to check on fetal growth and monitor other development milestones; it also provides the most accurate estimate for how many weeks pregnant you are and what your due date will be.
Week 4 of pregnancy
For example, a fertilised egg may have implanted in your womb just 2 weeks ago, but if the first day of your last period was 4 weeks ago, this means you're officially four weeks pregnant! Pregnancy normally lasts from 37 weeks to 42 weeks from the first day of your last period.
The best way to determine your conception date is with a pregnancy confirmation ultrasound. Early pregnancy ultrasounds can determine the age of your growing baby and when you likely conceived.
You can calculate your baby's estimated due date based on the date of the first day of your last menstrual period (LMP). Your baby will be 'due' around 40 weeks after the first day of your LMP. This method is particularly accurate if you have a regular menstrual cycle.
Ultrasounds in Later Pregnancy
As pregnancy progresses, the accuracy of an ultrasound for predicting due dates decreases. Between 18 and 28 weeks of gestation, the margin of error increases to plus or minus two weeks. After 28 weeks, the ultrasound may be off by three weeks or more in predicting a due date.
Between 22 0/7 weeks and 27 6/7 weeks of gestation, ultrasonography dating has an accuracy of ± 10–14 days 19.
Pregnancy Week 5. In week 5 of pregnancy, your baby is actually 3 weeks old and has finally "moved into" your uterus.
Your weeks of pregnancy are dated from the first day of your last period. This means that in the first 2 weeks or so, you are not actually pregnant – your body is preparing for ovulation (releasing an egg from one of your ovaries) as usual. Your "getting pregnant" timeline is: day 1: the first day of your period.
It can be confusing during the first month because pregnancy (which is an average of 40 weeks long) is actually measured from the first day of your last menstrual period. Even though you likely ovulated and conceived only two weeks ago, technically, you're considered to be four weeks along.
If you were having regular periods before pregnancy, your doctor will calculate your due date based off of your last menstrual period. This goes back to the fact that in order to get pregnant, your body ovulated—or released an egg—roughly in the middle of your cycle and it was fertilized by sperm.
The first day of your period is Day 1 of your menstrual cycle. Starting on the first day of your period, start counting. The day before your next period is the last day of your menstrual cycle. That's when you stop counting.
Conception usually occurs around 11-21 days after the first day of the last period of a woman who has a regular period. The estimation of conception date is based on this, but is rarely ever exact since it is difficult to know exactly when ovulation occurs.
The doctor has to guess on the conception date. In order to do so the doctor guesses the time of conception by utilizing the date of the last menstrual period. This day can be wrong by up to 2 weeks.
It is very common when scanning an early pregnancy to find that the due date does not match the menstrual history. Sometimes the dates can be more than a week off and sometimes even as much as 4 weeks.
Pregnancy is calculated from this day because each time a woman has a period, her body is preparing for pregnancy. Counting from the LMP, most women are pregnant an average of 280 days.
3 Early ultrasound due dates have a margin of error of roughly 1.2 weeks. After 20 weeks of pregnancy, your estimated due date shouldn't change based on an ultrasound because it will be less accurate.
Yes, although it's not very likely. If you have sex without using contraception, you can conceive (get pregnant) at any time during your menstrual cycle, even during or just after your period.
A normal cycle can be between 21 to 35 days, and some people can even have cycles that range outside of that. Regularity isn't that common, so there's a fair chance that the calculation will be off, but the last menstrual period measurement is still used because it's considered fairly reliable most of the time.
Usually, the sperm reaches the egg within 15 to 45 minutes of ejaculation. However, the process could be much longer than that if you haven't ovulated yet by the time you have sex, because sperm can live inside a reproductive tract and wait for an egg for up to five days.
In general, this doesn't happen a lot—but it usually depends on how your due date is calculated in the first place. “If dating is only based on the last menstrual period and a later ultrasound shows a discrepancy, then the due date may be changed,” Lamppa says.