How to calculate the due date
Release time : 03/22/2025 09:30:02
How is the estimated due date determined? The estimate due date is not a precise birth date, and its significance does not indicate that the child will definitely be born on the day of the estimated due date. Among women who give birth naturally, only about 5% are exactly at the estimated due date, while approximately 85% give birth within two weeks before or after the estimated due date, which is all within normal ranges.
How to calculate the estimated due date? 1. Last menstrual period method: Add 9 or subtract 3 from the number of months in the last menstrual period, and add 7 days (the day refers to the first day of the last menstrual period).
For instance, if the last menstrual period began on March 5 and ended on March 10.
Therefore, the estimated due date is December 12th.
Applicable Population: This method is applicable to pregnant women who can clearly remember their last menstrual period and have a normal menstrual cycle (28 days to 32 days).
In fact, there are many online calculators for estimated due dates or pregnancy calendars issued by hospitals, which all use this method.
2. B-ultrasound Data Calculation Method: By means of ultrasound examinations and measurements, such as the biparietal diameter, head circumference, femur length, abdominal circumference, etc., of the baby's body data (which is similar to adult's three-dimensional data), the estimated date of delivery can be calculated.
Below are the relevant B-scan data.
Pregnant women who can't understand it are not a problem.
Because the doctor will help you calculate the fetal age based on these data (the age of the fetus is calculated in weeks. Generally, the fetal age of 40 weeks is the expected date of delivery), you don't need to calculate yourself.
Generally, after the calculation is made, the doctor will indicate on the B-ultrasound sheet: gestational age ** weeks +* days.
GS-Fetal sac: Also called pregnancy sac, it is a small house that wraps the baby and amniotic fluid.
Generally, 35 days after menstruation stops, the fetal sac can be seen in the uterine cavity through B-ultrasound.
The diameter of the placental sac is about 2 cm at 6 weeks of pregnancy and about 5 cm at 10 weeks of pregnancy.
FE-Fetal buds: When the baby is not yet formed, it is just like a little bean that has just sprouted.
B-ultrasound can detect a uterine gestational sac at 6-7 weeks of pregnancy.
CRL-Head-hip length: It is the distance between the baby's head and buttocks, mainly used to determine the gestational age of 7 to 12 weeks of pregnancy.
Between 6-13 weeks, estimated gestational age (weeks)= head-hip length +6.5 (cm). BDP-Biparietal diameter of fetal head: The length of the widest part between the left and right sides of the fetal head.
It should reach 9.3 centimeters or more at full term.
According to the general rule, after 5 months of pregnancy, it basically matches the pregnancy month, that is to say, BPD is about 7.0 cm at 28 weeks of pregnancy (7 months), and about 8.0 cm at 32 weeks of pregnancy (8 months), and so on.
At the 8th month of pregnancy, an average weekly growth of about 0.2 cm is considered normal.
"If I can't remember my menstrual cycle, then please do me a favor," she said.
Pregnant women with irregular menstrual cycles can use ultrasound data to determine the size of the fetus and thus calculate the estimated date of delivery. The FL-Femur Length: This refers to the length of the fetus's thigh bone from the base of the femur to the knee joint.
Around the 20th week of pregnancy, it is common practice to measure FL (Femur length) to assess fetal development.
If the estimated due date calculated by ultrasound differs from that determined by menstruation, and the gestational age as measured by ultrasound is either one or two weeks larger or smaller, there is no need for concern. Some data may still change gradually. If it's smaller than expected, consume more food to catch up with the baby; if it's larger than expected, pay attention to controlling your diet and avoid overeating.
As long as it conforms to the menstrual cycle calculation method, everyone is ready to welcome the baby at 37 weeks. Therefore, there's no need to fret over whether the estimated date of delivery from a B-ultrasound matches the actual due date.
3. Other methods of calculating the estimated due date: Besides the two more convenient and accurate methods mentioned above, there is also the nausea count method (usually nausea begins after 6 weeks, but I personally believe that this can vary based on individual constitutions, so it's not always accurate), and the first fetal movement counting method (usually the first fetal movements occur between 16 to 18 weeks, but this method requires knowing about fetal movements beforehand, which is not accurate, and I don't recommend it). Is the estimated due date accurate? According to survey statistics, only about 56% of pregnant women give birth on the estimated due date. The estimated due date is just a rough timeframe for when a pregnancy will end, and the purpose of calculating the estimated due date is to prepare a mother-to-be for motherhood, not to determine exactly when delivery will happen.
When a baby is born, several factors can influence the timing of birth. These include conditions within the womb (such as the intrauterine environment), development of the fetus, physical health of the pregnant woman, and the actual circumstances of the pregnancy.
Generally speaking, labor within two weeks either side of the estimated due date is considered normal.
Clinically speaking, full-term fetus refers to the gestational age between 37 weeks and 42 weeks, and about 80%-90% of pregnant women give birth during this period.
Infants delivered less than 37 weeks are premature, accounting for about 5%-10%.
The younger the gestational age, the weaker the ability to live in premature infants.
What is the use of the expected date of birth refers to the day when the baby matures in the mother's body and is about to be born. Because that day has not yet arrived, we can understand it as the "expected date of birth". Since it is an estimate, it is definitely not 100% accurate.
The expected date of birth can remind you of the time range for the safe birth of the fetus, prepare for the baby in advance, and also has a positive reference for regular prenatal check-up data.
But don't look at the expected date of delivery so accurately.
By the 37th week of pregnancy, you should always be ready for delivery.
Frequently asked questions about the expected date of birth. How should the expected date of birth be calculated? The first type: I just discovered that I am pregnant and have no idea about the expected date of delivery. How should I calculate it? Mom website netizen H Aishang l officially certified intrauterine pregnancy. I am happy, but how to calculate the expected date of delivery? Please ask for help.
I would like to ask how to calculate the expected date of delivery? My menstruation is normal. My period came on March 29 and ended on April 4. So what month is my due date? Is it a baby horse or a baby sheep? The second type: The menstrual cycle is always inaccurate, and sometimes it is delayed by more than 10 days. How can this be calculated as the expected date of delivery? Babe's menstruation is usually delayed, sometimes by more than ten days or a month.
Due to the delay of more than 50 days, I went for a B ultrasound. The doctor told me that I was only about thirty days pregnant. So how should I calculate my due date? The third option: Pregnancy dating based on menstrual cycle and calculated based on B-ultrasound data don't match. Which one is correct? A netizen from MomNet zaizaijing asked which due date calculation should be used: the last menstrual period or the earliest B ultrasound report? The last menstrual period was on August 9th. According to this, the due date should be May 16th.
However, the doctor calculated my date according to the initial ultrasound report, which was for May 30th. The ultrasound showed a half-month smaller than the actual date.
Which is the correct estimated date of childbirth? The fourth option: For those undergoing in-vitro fertilization and embryo transfer, how should the estimated date of childbirth be calculated? How about Mamiao net user eyelash Yaoyao? How is the estimated date of childbirth calculated for IVF? If I had my egg retrieval on April 2nd, and I transferred the embryo on April 30th, what is the estimated date of childbirth? What if the baby hasn't given birth by the estimated date of childbirth? Many babies don't show any signs of labor until after their estimated date of childbirth, causing great concern among mothers.
In fact, if the baby is not born before 42 weeks, there's no need to worry too much. Pay attention to counting the fetal movements and communicate with your doctor for appropriate examinations.
Moms can also use the method of walking more after meals to let their baby not be a dropout and quickly start.
The medical information provided in this text is for reference only and should not be used as medical advice.
If you experience discomfort, it is recommended to seek medical attention immediately. The diagnosis and treatment should be based on a consultation with a healthcare professional in person.