Early fetal development

Baby development is a very complex process. From the moment the egg and sperm meet, your baby grows. This early stage of development lays the foundation for a healthy pregnancy and childbirth. It is important to be informed in order to resolve any problems associated with early fetal development.

If a possible complication of early fetal development is suspected, your doctor will use a combination of blood tests and ultrasound to make a definitive diagnosis. A blood test can be used to monitor hCG levels and progesterone levels. Ultrasound can be used to visually see what development is taking place in the womb and measure progress.

Because every woman is different and every pregnancy is different, this information should be used as a general guide to healthy pregnancy development, although early fetal development may vary depending on the health of the mother or her pregnancy, ovulation miscalculation. Gestational age is the age of pregnancy from the last normal menstrual cycle, while fetal age is the actual age of the growing baby.

Most references to pregnancy usually refer to gestational age rather than fetal developmental age, but we have included both to make it clear what stage of development this is in.

Gestational age weeks 1 and 2 (fetal age: conception)

At this point, the menstrual period has just ended and your body is getting ready to ovulate. Most women ovulate about 11 to 21 days after the first day of their last period. During intercourse, hundreds of millions of spermatozoa are released into the vagina. The sperm will pass through the cervix and into the fallopian tubes.

During conception, the sperm enters the egg and creates a unique set of 46 chromosomes called a zygote, the basis of a new person. A fertilized egg, called a morula, travels through the fallopian tube to the uterus over several days and divides into cells (many chromosomal abnormalities occur in this division process).

The morula develops into a blastocyst and ends up in the uterus. On the 6-12th day after conception, the blastocyst integrates into the uterine mucosa and enters the embryonic stage.

Gestational age weeks 3-4 (fetal age: 2 weeks)

The first change that can be seen on a vaginal ultrasound at this time is the “decidual reaction,” which is thickening of the endometrium. The lining of the endometrium thickens as the blastocyst penetrates into it. This can't always be detected by ultrasound - sometimes it takes a special eye or very good equipment to see this "reaction" in the endometrial mucosa.

A key fact to remember when choosing an ultrasound is that a transvaginal ultrasound can detect development in the uterus about a week earlier than a transabdominal ultrasound.

HCG pregnancy hormone

After implantation, the pregnancy hormone human chorionic gonadotropin (hCG) is produced and begins to increase. This hormone will signal that you are pregnant on a pregnancy test. HCG can be detected by two different types of blood tests or a urinalysis.

A quantitative blood test measures the exact amount of hCG in the blood, while a qualitative hCG blood test simply detects the presence of hCG.

Doctors often use a quantitative test if they are closely monitoring the progress of a pregnancy. After implantation, the hormone levels will begin to increase and should increase every 48-72 hours for the next few weeks.

Progesterone

The follicle from which the egg is released is called the corpus luteum. It releases progesterone, which helps thicken and prepare the uterine lining for implantation. The corpus luteum produces progesterone for about 12-16 days (the luteal phase of your cycle).

When the egg is fertilized, the corpus luteum will continue to produce progesterone to develop the pregnancy until the placenta takes over around the 10th week. Progesterone is a hormone that helps maintain pregnancy until birth.

Sometimes the inability of the corpus luteum to adequately support a pregnancy with progesterone can lead to early pregnancy loss. Progesterone suppresses immune responses, lowers prostaglandin levels, and prevents uterine contractions from starting.

Gestational age week 5 (fetal age: 3rd week)

Around 5 weeks, the gestational sac is often the first thing most transvaginal ultrasounds can detect. This is visible before a recognizable embryo can be seen. During this period, the yolk sac can be seen inside the fetal egg. The yolk sac will be the main source of nutrients for the developing fetus.

Human chorionic gonadotropin (hCG) levels may vary slightly at this point. Anything between 18 and 7340 mIU/mL is considered normal at 5 weeks. Once levels are at least 2000, some type of development is expected to be visible in the uterus with a high-resolution vaginal ultrasound.

If transabdominal ultrasound is used, then some development should be observed when the hCG level reaches 3600 mIU / ml. Although development can be seen earlier, these levels indicate when something should be seen.

Progesterone levels can also vary greatly during this stage of pregnancy. They can range from 9 to 47 ng/ml during the first trimester, with an average of 12 to 20 ng/ml during the first 5-6 weeks of pregnancy.

Along with hCG and progesterone levels, this is not the only value that can predict a successful pregnancy outcome. It's more important to evaluate two different values to see if the numbers increase. HCG levels should rise by at least 60% every 2-3 days, but ideally double every 48-72 hours.

Progesterone rises quite differently from hCG levels, averaging 1-3mg/mL every other day until it reaches its peak for that trimester. In situations where there is concern about an ectopic pregnancy or miscarriage, hCG levels often start normally but show little or no increase at all, and progesterone levels will be low at the start.

Gestational age week 6 (fetal age: 4 weeks)

Between 5.5 and 6.5 weeks, the fetal pole or even the fetal heartbeat can be detected using a vaginal ultrasound. The fetal pole is the first visible sign of the developing embryo. This pole structure actually has a certain curve, with the head of an embryo at one end and what looks like a tail at the other end.

The fetal pole now allows measurements from the crown to the sacrum, so pregnancy dating can be a little more accurate. The fetal pole can be seen when the crown-sacrum is 2–4 mm long, and the heartbeat can be seen as a steady beat when the crown-sacrum reaches 5 mm.

If a vaginal ultrasound does not show the fetal pole or cardiac activity, a second ultrasound should be performed after 3-7 days. Because pregnancy dating can be erroneous, it would be too early to make a clear diagnosis of pregnancy outcome at this stage.

Gestational age week 7 (fetal age: 5 weeks)

As a rule, from 6.5 to 7 weeks, a heartbeat can be detected and viability can be assessed. A normal heart rate at 6-7 weeks would be 90-110 beats per minute. The presence of a fetal heartbeat is a sure sign of a healthy pregnancy.

Once a heartbeat is detected, the chances of continuing the pregnancy range from 70 to 90% depending on the type of ultrasound used. If the embryo is less than 5 mm from the crown to the sacrum, it may be healthy, with no signs of a heartbeat, although a follow-up scan 5 to 7 days later should show cardiac activity.

If your doctor is concerned about a miscarriage, egg damage, or ectopic pregnancy, the gestational sac and fetal pole (if visible) will be measured to determine what type of development to watch for. According to the recommendations, if the size of the ovum is > 16-18 mm without a fetal pole, or if the fetal size is 5 mm without a heartbeat (according to vaginal ultrasound), a diagnosis of miscarriage or egg change is made.

If the fetal pole is too small for an accurate measurement, a rescan should be performed after 3-5 days. In the absence of a fetal pole, additional tests should be performed to exclude the possibility of an ectopic pregnancy.

Gestational age weeks 8 and 9 (fetal age: 6-7 weeks)

At this stage of pregnancy, everything that an adult has is present in a developing embryo. The embryo has reached the end of the embryonic stage and is now entering the fetal stage. Ultrasound should detect a strong fetal heart rate with a heart rate of 140 to 170 beats per minute at 9 weeks.

If no palpitations are detected at this stage, another ultrasound may be performed to check for fetal viability.

If the pregnancy has been diagnosed as not viable, most doctors will give you a choice: wait to see if the miscarriage occurs naturally (in the absence of other health problems) or undergo a curettage procedure. About 50% of women do not undergo curettage during early pregnancy loss.

HCG levels peak around 8-12 weeks of gestation and then decline, remaining at a lower level for the rest of the pregnancy. If levels are uncertain, ultrasound should be used to diagnose pregnancy outcome. Ultrasound results are much more accurate in diagnosing pregnancy viability after 5-6 weeks of gestation than hCG levels.