1.Last menstruation
The rule for calculating the week of pregnancy is to start calculating from the point of last menstruation as 0:00. In fact, the week of pregnancy calculated from the last menstrual period, the period from 0 to 2 weeks of pregnancy, pregnancy has not yet occurred at all. Instead, at 0 weeks of gestation, the egg that will unite with the sperm has already started to activate and develop. At 2 weeks of gestation, this egg will develop into a dominant follicle and unite with the sperm to form a fertilized egg, and it is at this time that gestational age begins, which means that 2 weeks of gestational age = 0 weeks of gestational age. The first two weeks of gestational age is not the state of pregnancy, and it is understood that gestational age is actually calculated from the development of the egg.
Doctors do not like to calculate the gestational age in months, because all clinical diagnoses and clinical management principles are based on weeks, so I hope that you will keep your mind in line with the doctor’s mind and keep in your head as many weeks of pregnancy as possible, and not the months of pregnancy.
The gestational age of 280 days (= 40 weeks) is the period of pregnancy and delivery. 37 to 42 weeks of delivery are considered full term, less than 37 weeks is considered premature, and more than 42 weeks is considered overdue. The most appropriate gestational week for delivery is 39 to 41 weeks.
For people with regular menstrual cycles, it is very easy and accurate to calculate the gestational age by taking the last menstrual period as the starting point. Therefore, we hope that women will make it a habit to record their menstrual periods when planning their pregnancy. Remember, it’s the first day of your period, not the day your period clears.
Any other way of accounting for the week of pregnancy will eventually be corrected to the last menstrual expression pattern.
2. Ultrasound calculation
The ultrasound accounting of the gestational week must be seen according to the ultrasound of early pregnancy. The ultrasound in the middle and late stages of pregnancy has no reference value. Because in the early stage, there is not much difference, all are developed from a cell of the same size, the more the difference grows later. This should be easy to understand, the size difference between newborns at birth is only two or three centimeters, and in adulthood it may be tens of centimeters, just as we cannot judge a person’s age by his or her height.
We usually refer to the ultrasound report up to 11 weeks, and the simpler way to calculate is that the fetal bud length is about 1mm per day, and the gestational week when the fetal bud is visible on ultrasound is about 6-7 weeks, which is estimated to be 6 weeks + 5 days, so the presumed gestational week is about “6 + (5 + fetal bud length mm) / 7” weeks.
When the gestational week is small, the length of the fetal germ will be written on the ultrasound sheet. If the gestational week is a little larger and the embryo grows to several tens of millimeters, the ultrasound report will write “top-rump length”, so “top-rump length” = “fetal germ length”.
In addition, the time when the primitive heart tube beats is fixed, and the fetal heart can be seen at 6 weeks, so if the ultrasound can see the fetal heart beats, it means the embryo is at least 6 weeks old. (With a good ultrasound, you can see it at more than 5 weeks)
If the ultrasound report of early pregnancy is not available, the ultrasound of middle and late pregnancy will also estimate the pregnancy week according to the size of the fetus, but the accuracy of this estimation is greatly reduced, the later the error is, the greater the error is, and the difference between the actual pregnancy week and a week or two is not a problem.
3. Embryo implantation date
For IVF, the gestational week calculation is based on the date of embryo implantation. Usually the embryos are transferred on the 2nd or 3rd day of culture, or possibly the 5th day of transfer, which means that the embryos will be allowed to implant. Normally, natural conception usually occurs on the 6th to 7th day after the formation of the fertilized egg. After the embryo is transferred, it will take a little bit of time until successful implantation, so although the embryo has been developing in vitro for a few days at the time of transfer, the implantation itself is still full of uncertainty, so we will still take the date of transfer as the starting point of gestational age and push forward 14 days as the starting point of the gestational week.
4. Day of ovulation
If you monitor ovulation, you can also calculate it in this way. Usually people who monitor ovulation will also know the date of intercourse, and the formation of a fertilized egg occurs within 48 hours after ovulation. We can take the date of ovulation 14 days before the last menstrual period as the starting point of the pregnancy week calculation, but of course this date may not be the real last menstrual period.
5. Date of intercourse
If you are very sure and certain that you had intercourse only once in that month, and you have not had intercourse since then, and you remember the date clearly, you can consider this day as the day of fertilization, and push forward 14 days to the last menstruation as the starting point of the pregnancy week calculation.
6. Symptoms of pregnancy
This is not used to calculate the week of pregnancy, because the symptoms are too subjective and too different to be reliable, but we can verify our calculated week of pregnancy and compare the time of appearance of pregnancy symptoms to see if they match the week of pregnancy.
For example, early pregnancy reactions (nausea, vomiting, etc.) usually appear around 40 days and significantly reduce or disappear between 11 and 12 weeks, and the symptoms of frequent urination mostly appear around 60 days, and most of them disappear after 12 weeks when the uterus is out of the pelvis. The earliest fetal movement can appear in 16 to 18 weeks, later about 20 weeks perceived fetal movement, if the difference is too big, we should suspect whether the pregnancy week is miscalculated.
1.How to calculate the week of pregnancy when the menstrual cycle is long? How to calculate the week of pregnancy if the cycle is too short?
For the calculation of the gestational week, we assume that the menstrual cycle is 28 days, and then start the calculation from the last menstrual period. In fact, the real data that can accurately account for the week of pregnancy would be the date of the formation of the fertilized egg, which is not known. Therefore, we can only calculate it by projecting the day of ovulation.
The first half of the menstrual cycle is the follicular phase and the second half of the cycle after ovulation is the luteal phase, which is very constant because the menstrual corpus luteum has a life span of only 14 days and after 14 days, if you are not pregnant, you will have your period. Therefore, people with long menstrual cycles actually have a long follicular phase, while those with short cycles actually have a short follicular phase. Therefore, for people with particularly long or short menstrual cycles, we can recalibrate the pregnancy week according to the characteristics of the period cycle.
2. How to calculate the pregnancy week with regular menstruation?
First of all, we should clarify how to count irregular menstruation. Menstrual cycle fluctuations within 1 week are considered regular, but if the fluctuation is more than 7 days, it is considered irregular. For example, if your period is 5 days early and 4 days late, it is irregular, but occasionally 2 days early or 2 days late is still considered regular.
For irregular cycles, the ultrasound of early pregnancy is preferred to verify the week of pregnancy, as doctors are more willing to trust objective data.
Ultrasound in early pregnancy > date of intercourse > ultrasound in mid to late pregnancy
Intercourse date and ultrasound in mid and late pregnancy can corroborate each other and complement each other, no method is very accurate.
3.Menstruation is very messy or I can’t remember the last menstruation, the date of intercourse is not available, and the ultrasound of early pregnancy is not available, what should I do?
There is no way, how to calculate can’t be accurate. We can only ask you to carefully recall the time when the various symptoms of your pregnancy appeared, and it is best to tell the month, day and year, and then confirm each other according to the earliest ultrasound that we can find. This is the only way out.
So especially to solemnly remind every memory never remember the menstruation of the girls, do not embarrass the doctor, long snack it!
4.Why does the week of pregnancy reported in the ultrasound not match with my week of pregnancy?
”I am obviously 25 weeks, but why does the ultrasound sheet say “equivalent to 24 weeks intrauterine pregnancy”?”
The ultrasound is based on the fetal body measurements at the time of the ultrasound, and is based on the size of the fetus.
”So my fetus is small, what should I do? How can I eat to make the fetus bigger?”
My friend, the bigger the fetus, the better! The small size of the fetus does not mean that it will grow if you eat more; more often than not, the small size of the fetus is actually due to the fact that the fetus does not grow much in the first place. The fact that it grows slowly is often due to its “internal” factors, not something we can influence from the outside. And, not every fetus grows at the same rate, not every fetus is the same size, the normal value is not a fixed value, but a range, as long as it continues to grow, it does not matter, okay!
One more thing, do you think the ultrasound is that accurate? Don’t think too much, if the ultrasound is omnipotent, then how can there be deformities that the ultrasound can’t find? So the ultrasound measurement out of the big and small, may not be accurate.