Pregnancy / Childbirth

Date of delivery - according to menstruation or ultrasound?


There is a view that ultrasound examination is more reliable for the assessment of pregnancy age than the given date of last menstruation. Why? Research suggests that usually the delivery period calculated from menstruation adds to pregnancy age around 2.8 days, which is most often associated with delayed ovulation. Therefore, the date of delivery with ultrasound is to be more reliable, but is it really so?

Date of delivery and menstruation

The age of pregnancy and date of delivery is usually determined based on the first day of your last menstrual period - all because determining when ovulation and de facto insemination is very difficult. However, the date of your period is usually easier to determine.

If the expectant mother has had regular cycles and knows the date of the last menstrual period, the date of delivery and the age of pregnancy can be determined on this basis.

Date of delivery and ultrasound examination

During ultrasound, you can estimate the age of pregnancy by assessing the size of the embryo, and later with the development of the child - the length of individual parts of the body. The toddler can be measured as early as 5-6 weeks of pregnancy. At this stage, ultrasound measurement is the most accurate.

Over time, when they come to the fore individual features and pace of development - assessment of pregnancy age based on the size of the child can be much more difficult. In addition, the problem is often caused by the growth of the uterus and its size - which may not correspond to the age of pregnancy.

During ultrasound examinations, the most important measurements include assessment of the size of the head, stomach and legs.

It is believed that there may be a difference between the age of pregnancy with ultrasound and menstruation. If it fits within two weeks, is considered the norm.

You should also be aware that the date of delivery may vary depending on whether the size of the head, tummy or leg length is taken into account. In all cases, the age of pregnancy is different. It's completely normal - each child has slightly different proportions and can develop a little differently. If the doctor sees no reason for concern, you do not worry.

The date of delivery from the ultrasound and the period of menstruation differ

The date of delivery calculated on the basis of menstruation and ultrasound may differ.

If it is different already in 1 trimester of pregnancy, the cause may be irregularity of monthly cycles. It also often happens that the expectant mother is not sure of the date of the last menstrual period, so the problems with assessing the age of pregnancy on its basis are understandable.

If the two dates - determined from menstruation and ultrasound - differ by at least two weeks in the second trimester, the reason may be the child's not quite good condition. A baby in his tummy may not receive all the important nutrients, and the problem may also be disturbed umbilical cord blood flow. In this situation, the doctor usually orders a specialized examination (Doppler scan) to assess the umbilical cord blood flow.

Different dates of delivery in second trimester - different from the date of menstruation and ultrasound - can mean gestational diabetes. In diabetes the child is often larger than the actual age of pregnancy indicates. In this situation, your doctor may recommend the optimal diet as well as additional tests.

IN third trimester of pregnancy assessment of pregnancy age based on individual data obtained during the measurement of a child may be difficult. The fetus is often so arranged that the measurements are not simple. To make this task as easy as possible, it is usually considered at this stage femur length.

If the baby does not develop properly, its size does not correspond to the age of pregnancy, or other alarming signals appear, the doctor may recommend early termination of pregnancy, either by caesarean section or induction of delivery.

Here is the pregnancy week calculator, thanks to which you will find out at what stage of pregnancy you are.