Pregnancy / Childbirth

How to determine the date of conception?

How to determine the date of conception?



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It is not often that a woman can determine the day on which fertilization took place. If before did not observe her menstrual cycle, calculators that calculate the approximate date of conception can come in handy. The fetal age will be more accurately determined by the doctor during ultrasound examinations. And although the date of conception is the correct beginning of pregnancy, the so-called gestational age is more important for the doctor. It is on its basis that the date of delivery is determined.

Let's start from the beginning. Fertilization can only occur during about one day, during the ovulation phase, which usually runs on day 14 of the cycle. It should be remembered that fertile days start earlier - sperm can survive in the woman's body from 3 to 5 days, and the egg up to two days after leaving the ovary.

How to recognize ovulation?

Many women can feel the moment of ovulation - appears then lower stomach pain and breast hypersensitivity. It can also come to a slight increase in temperature around the cervix, and immediately after ovulation - to a slight increase in body temperature.

They are noticeable changes in cervical mucus - a few days before ovulation it becomes transparent, and just before ovulation itself is more dense. Therefore, it is worth conducting observations of the cycle and calendar entries, because it will later be more likely to determine the date of conception.

Age of pregnancy and date of delivery

Menstruation is much easier to notice than ovulation and it is on its basis that the so-called age of pregnancy. This is Naegele's rule according to which pregnancy lasts 280 days or 9 months from the start of the last menstrual period. In fact, it is two weeks shorter and lasts 266 days from ovulation. It is assumed that the menstrual cycles were regular and lasted 28 days, and ovulation took place on the 14th day. It is the age of pregnancy that the doctor uses to keep the pregnancy card and set the date of delivery. Fertilization age, in turn, determines the exact age of the fetus and is counted from the moment when conception actually took place.

It is worth noting that in Only around 5% of children are born on the date of delivery based on the gestational age. 90% are born within 2 weeks before and up to 2 weeks after the deadline. However, it is very important for a woman to know exactly when to expect a delivery, as well as for the safety of the child, that the delivery date should not be too late or too early.

How to calculate the conception date yourself?

Many pregnancy calculators are available on websites to help you calculate the approximate date of conception. Most often you need data such as: date of the start of the last bleeding, length of the menstrual cycle and sometimes also the length of the luteal phase. They also allow you to determine the date of conception based on the date of delivery. However, these are all estimates that assume pregnancy lasts 280 days from the date of the last menstrual period or 266 days from the date of ovulation. They need to be modified if the cycles are irregular and do not last 28 days.

Fetal age determined by the physician

Ultrasound (ultrasound) performed by a gynecologist gives more certainty about the moment of pregnancy. This applies especially to tests during the first trimester of pregnancy. Later, fetuses grow at a different pace, which means that ultrasound examinations in the second and third trimester of pregnancy no longer allow such accurate and reliable age determination. In the case of ultrasound examinations, 2 weeks are added to the fetal age obtained, which usually pass from the first day of menstruation to ovulation (and fertilization), thus obtaining an inflated fetal age.

The longer the pregnancy lasts, the greater the discrepancy between the age of the fetus and the age of pregnancy can be, even 3-4 weeks. If in the first trimester ultrasound examination it turns out that the pregnancy age differs from that calculated based on the last menstrual period by more than a week, the doctor will change the method of calculating the pregnancy age to the one determined in the ultrasound examination. This is especially the case when the menstrual cycles before pregnancy were very irregular.

Determining paternity based on the date of conception?

When a woman finds out that she is pregnant, and before she did not analyze the cycle carefully, she often wants to find out exactly on which day the conception took place. It happens that he wants to determine in this way who the father of the child is, for example, when she had more than one partner. However, it should be remembered that most often the exact date of conception is not possible to determine with 100% certainty. Usually, only the time period during which fertilization could occur can be determined. The date of conception does not necessarily coincide with the date of intercourse. It is not possible, therefore, to reliably establish fatherhood. The unambiguous answer in this case will be given by genetic tests, performed during pregnancy or after childbirth.