Fetal Development

Embryology is the study of human development from a single fertilized egg to delivery of a healthy baby; therefore, it is a critical field of study for not just pregnancy, but all of human health.

Researchers believe that better understanding how and when certain events occur during early development can potentially lead to the prevention of miscarriage, birth defects, metabolic disorders, stillbirth, and even childhood diseases. Embryology advances could also improve treatments during adulthood.

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Fetal Development Introduction

Embryos develop very quickly in early pregnancy and structures can grow within hours. As the embryo becomes a fetus, development slows down (as it is almost complete) but growth speeds up as the fetus increases in length and weight.

Development (in Relative Order of Development)

Fertilization and Implantation

Fertilization, or conception, occurs within 12 to 24 hours after ovulation; the blastocyst implants around 6 to 7 days later. Another 24 to 48 hours for HCG to circulate in the blood, and a pregnancy test will become positive.

Human Chorionic Gonadotropin (HCG)

HCG levels are important in determining the health of the fetus in early pregnancy. Higher or lower than expected levels at certain points during pregnancy can be associated with certain complications.

Due Date and Gestation

Current evidence-based information indicates women should focus more on a delivery range that equates to 14 days on either side of their given due date, or 28 days in total, in which almost all women are expected to deliver.

Amniotic Fluid

Amniotic fluid is a key marker of fetal health during pregnancy and a direct route to the fetus. The amount of amniotic fluid – and its contents – can provide clues for proper organ development, as well as potential complications or birth defects.

Placenta

The placenta is one of the most powerful temporary organs of the human body. It releases its own hormones, provides nutrients to the fetus, filters out waste, and establishes an intricate network of blood vessels that connects fetal health to the health of the mother.

Cardiovascular System

Unlike all other organ systems in the embryo, the cardiovascular system needs to function almost as soon as it starts to form. The heart starts beating at the very start of the 5th week.

Umbilical Cord

The umbilical cord begins to develop early in pregnancy and is complete by 12 weeks. The cord plays an important role in the transfer of nutrients to the fetus and the transfer of waste away from the fetus (and to the placenta).

Neural Tube

The neural tube develops and closes very early in pregnancy – by the 6th week. Failure of this complex process to occur correctly results in one or more neural tube defects (NTDs).

Vitamin B9 (Folate/Folic Acid)

Supplementation of folic acid is recommended (even before pregnancy) for the prevention of neural tube defects. Folic acid may also play a role in successful implantation and placental development.

Brain

The amount of time required for full brain development is longer than any other organ. While the brain begins to develop very early in pregnancy, it grows and “fine tunes” the entire 9 months and beyond – into adulthood.

Bladder and Kidneys

Bladder and kidney function can be assessed early in pregnancy to determine fetal well-being. An early second trimester ultrasound can show both the bladder and the urine it holds.

Gastrointestinal Tract

The GI tract of the fetus grows rapidly in the first trimester, and by 12 to 13 weeks of pregnancy, some abdominal organs have completed three 90-degree rotations inside (and outside) of the body.

Arms, Hands, Legs, and Feet

The development of fetal limbs begins around 5 weeks of pregnancy. The upper limbs are always a few days ahead of lower limb development, to include legs, feet, and toes, but can all be well observed via ultrasound by 10 weeks of pregnancy.

Face

Development of the face is very complex, involving growths, swellings, expansions, mergers, and fusions of various structures in the same rapid time frame in early pregnancy. While genetics controls most of this process, outside factors also play a role.

Eyes (and Vision)

Eye development begins early and continues throughout gestation, with protective functions and possible wound healing properties.

Ears (and Hearing)

While the structural aspect of the ear is usually complete before the third trimester, the development of the auditory system – hearing – develops from the late second trimester to term.

Reproductive System

The sex of a fetus is determined at conception, based on whether an X or Y sperm fertilized the egg (X and Y sperm swim at the same speed). Hormonal triggers then further the development of male or female reproductive organs.

Respiratory Tract

Although lung development and growth begins early in pregnancy, the structural changes required for breathing do not occur until the final few weeks of pregnancy.

Hair, Skin, and Nails

The development of hair and its different types serve very specific purposes during fetal growth and development and also reveal information about the baby's health.

Movement

Fetal movement is a positive sign of healthy growth and development and proves the fetus is growing in both size and strength.

Screening Tests

Various screening tests are recommended during the first and second trimesters that normally include ultrasound examinations and lab/blood work. These tests, taken together, can evaluate a fetus’ risk for one or more birth defects.

Ultrasound

Ultrasounds are commonly used in obstetrics. Most women will receive two to three of these examinations during their pregnancy, sometimes more if monitoring is required.

Possible Complications

First Trimester Viability

An early ultrasound carries the risk of uncertainty – being told a miscarriage may or may not occur. An early ultrasound can lead to a diagnosis of potential miscarriage that turns out to be viable, as well as a viable pregnancy that later miscarries.

Birth Defects

It is estimated that birth defects affect an average of 3% of all pregnancies, which includes both structural and functional defects; approximately 7,000 different types have been identified.

Bleeding (Vaginal)

Vaginal bleeding is very common in pregnancy, especially in the first trimester. However, bleeding does not always indicate a serious problem and does not always lead to pregnancy loss.

Pregnancy Loss (Overview)

Although not all miscarriages are recognized, early pregnancy loss is very common and affects many women, regardless of age, race, ethnicity, weight, overall health, and number of prior pregnancies.

Causes of Pregnancy Loss

Miscarriage is now considered multifactorial – meaning that it is more than likely multiple factors act to cause pregnancy loss, most of which are completely out of a couples’ control.

Management of Miscarriage

Women have several options for the management of miscarriage, a decision that is completely up to them, after a thorough risks and benefits discussion with their HCP.

Ectopic Pregnancy

Ectopic pregnancy occurs when a fertilized egg implants in a uterine structure other than the uterine lining (decidua), such as the cervix or Fallopian tube.

Molar Pregnancy

Molar pregnancies, when abnormal trophoblastic tissue grows into the uterus, are part of a category of conditions known as Gestational Trophoblast Disease (GTD) and are considered very rare.

Dilation and Curettage (D&C)

Dilation and curettage (D&C) is the most common surgical procedure performed by gynecologists. It is considered safe, effective, and carries a low complication rate.

Fetal Development

Development (in Relative Order of Development)

Possible Complications

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