What causes fetal arrest?

Pregnancy is a very important thing for women. The whole process will last for ten months. It is hard but happy. The two most undesirable things during pregnancy are miscarriage and fetal arrest. Fetal arrest is more despairing than miscarriage. Even if there is no miscarriage, the fetus stops developing, which makes anyone heartbroken. Understanding the main causes will help us take precautions. So, what causes fetal arrest? Let’s take a look below.

Fetal arrest refers to the cessation of embryo development due to some reason in early pregnancy. Ultrasound examination may show an irregular fetal bud or fetal shape in the gestational sac, no fetal heartbeat, or a withered gestational sac. Clinically, it falls into the category of miscarriage or stillbirth. There are many reasons for fetal growth retardation. More than 90% of them are related to abnormalities of the embryo itself. In a few cases, they are related to luteal insufficiency, hyperprolactinemia, abnormal thyroid function, and diabetes.

Endocrine disorders

Embryo implantation and continued development depend on the coordination of a complex endocrine system. Any abnormality in any link can lead to miscarriage. During the early development of the embryo, three important hormone levels are required: estrogen, progesterone, and human chorionic gonadotropin. As for the mother, if her own endogenous hormones are insufficient, it cannot meet the needs of the embryo and may cause embryo arrest and miscarriage. The most common of these is luteal dysfunction, which can cause delayed endometrial development and a short luteal phase, thereby affecting the implantation of the fertilized egg or early pregnancy miscarriage. People with luteal insufficiency are often accompanied by other glandular dysfunctions, such as hyperthyroidism or hypothyroidism, diabetes, relative androgenism and hyperprolactinemia. These factors are not conducive to embryonic development and are closely related to miscarriage.

Uterine abnormalities

Both the internal environment of the uterus and the overall environment of the uterus may have an impact on the embryo. The internal environment is the endometrium. If it is too thin or too thick, it will affect implantation. About 10% to 15% of miscarriages are caused by uterine defects. Common ones include (1) congenital abnormalities of the Müllerian duct, including unicornuate uterus, didelphic uterus, septate uterus, and bicornuate uterus, which result in a narrow uterine cavity and restricted blood supply. Abnormal development of the uterine arteries can lead to asynchrony of decidualization and abnormal implantation. (2) Intrauterine adhesions, which are mainly caused by intrauterine trauma, infection or residual placental tissue, leading to intrauterine adhesions and fibrosis. Hinders normal decidualization and placental implantation. (3) Uterine fibroids and endometriosis cause reduced blood supply, leading to ischemia and venous dilatation, asynchronous decidualization, abnormal implantation, and hormonal changes caused by fibroids, which can also cause pregnancy failure. (4) Congenital or traumatic cervical relaxation and abnormal cervical development caused by intrauterine treatment with diethylstilbestrol often lead to mid-term miscarriage.

Chromosome problems

If the chromosomes are abnormal, it may cause the embryo to not develop and lead to early miscarriage. Chromosomal abnormalities include quantitative and structural abnormalities. Quantitative abnormalities can be divided into aneuploidy and polyploidy. The most common abnormal karyotype is aneuploid trisomy, and trisomy 16 accounts for 1/3 and is often lethal. 25-67% of pregnancies with trisomy 21, 4-50% of pregnancies with trisomy 13, and 6-33% of pregnancies with trisomy 18 are bound to result in miscarriage. Others include haploid (45, XO) and tetraploid, which result in embryonic underdevelopment due to abnormal cleavage. Structural abnormalities include deletions, balanced translocations, inversions, overlaps, etc.

If one of the spouses has a balanced chromosomal translocation, it is easy for the embryo to have chromosomal abnormalities and cause embryonic arrest. The mechanism by which the embryo's chromosomal abnormalities occur is that when the couple's chromosomes fuse, chromosomal fragments are easily lost or duplicated, which leads to chromosomal abnormalities in the fertilized egg and failure to develop normally, which can lead to miscarriage, stillbirth, and deformed babies. Therefore, couples with chromosomal translocation need to undergo prenatal diagnosis in the second trimester to prevent the birth of children with chromosomal diseases. Theoretically, couples with chromosomal abnormalities have the chance of giving birth to normal karyotype and carrier babies. Prenatal diagnosis can be performed on these couples to ensure the birth of normal babies.

Abnormal genetic material carried by sperm can cause embryonic arrest, but abnormal sperm refers to the appearance of sperm and not the genetic material carried by sperm. Sperm morphology assessment is used to evaluate male fertility. Abnormal sperm refers to sperm that has no chance of meeting the egg under natural conditions. Therefore, it does not matter whether the abnormal sperm carries normal genetic material. Therefore, there is no relationship between abnormal sperm and spontaneous abortion. The sperm deformity rate is a percentage of semen indicators and must be evaluated in conjunction with the total number of sperm when evaluating the sperm deformity rate.

Immune factors

Embryonic arrest caused by immune factors is relatively rare and difficult to diagnose. The immunology theory refers to the fact that after a mother becomes pregnant, the fetus is considered an allogeneic transplant because it is a combination of the parents' genetic material and cannot be exactly the same as the mother. The immune incompatibility between the mother and the fetus causes the mother to reject the fetus. However, we currently have no way of determining whether the cause of the arrest is due to the mother's rejection of the embryo. However, logically speaking, if embryonic arrest is caused by maternal rejection, it should occur relatively early, rather than after the fetal heartbeat is detected. Blocking antibodies are only a control indicator after immunotherapy and cannot be used as an etiological diagnosis of embryonic arrest. The vast majority of women are negative for blocking antibodies during the non-pregnancy period, and even in the second trimester, only a few women have detectable blocking antibodies in their bodies.

Reproductive tract infection

In addition to the above factors, early pregnancy miscarriage caused by infection has received increasing attention from scholars at home and abroad. Severe TORCH infection in early pregnancy can cause fetal death or miscarriage, and milder infection can also cause fetal malformations. Studies have shown that cytomegalovirus can cause delayed abortion, intrauterine fetal death, etc. After the mother is infected, the pathogens can infect the placenta through the blood, causing damage to the chorionic and capillary endothelium, destroying the placental barrier, and the pathogens enter the fetus, causing miscarriage, embryonic development cessation, and fetal malformations. In recent years, many studies have shown that mycoplasma infection may be related to the cessation of embryonic development. However, some scholars have proposed that mycoplasma may be a normal flora of the human body. Mycoplasma found through screening in the recurrent miscarriage group can only be called mycoplasma presence rather than mycoplasma infection.

Environmental factors

Changes in physiological state during pregnancy cause significant changes in the mother's absorption, distribution and excretion of therapeutic drugs and various environmental harmful substances. In the early stages of development, the embryo is extremely sensitive to the effects of therapeutic drugs and environmental factors. At this time, various harmful factors can cause damage to the embryo or even loss. Many drugs and environmental factors are important factors causing early embryonic death or fetal malformations. Environmental hormones can directly act on the central nervous endocrine regulatory system, causing disorders in reproductive hormone secretion, decreased fertility and abnormal embryonic development. There are many environmental factors that cause miscarriage, including physical factors such as X-rays, microwaves, noise, ultrasound, high temperature, and heavy metals such as aluminum, lead, mercury, and zinc that affect the implantation of fertilized eggs or directly damage the embryo and cause miscarriage. Various chemical drugs such as dichloropropane, carbon disulfide, anesthetic gases, oral antidiabetic drugs, etc. can interfere with and damage reproductive function, causing embryo miscarriage, stillbirth, deformity, developmental delay and functional disorders. And bad living habits such as smoking, alcoholism, coffee, drugs, and certain medications all affect early embryonic development.