What causes threatened miscarriage?

One of the most concerned questions is: Why does threatened abortion suddenly occur after pregnancy? This is a question that is difficult to answer systematically, because up to now, many causes are still uncertain, but the causes revealed so far are roughly as follows:

Threatened abortion refers to the manifestation of miscarriage, but after the treatment of fetal preservation, the pregnancy may continue. It often occurs in the early stage of pregnancy, with mild intermittent uterine contractions, with or without a small amount of vaginal bleeding. It is called threatened abortion. Early threatened abortion occurs within 12 weeks of pregnancy, and late threatened abortion occurs between 13 and 27 weeks. Pelvic examination shows that the cervix is ​​not dilated, the fetal membranes are intact, no pregnancy products are discharged, the size of the uterus is consistent with the gestational age, and the B-ultrasound may show a trend of shortening of the cervix. If not treated in time, it may develop into inevitable miscarriage. Since 62% of miscarriages occur before 12 weeks of pregnancy, when the signs of threatened abortion appear in the early stage, sufficient vigilance and attention must be paid. The causes revealed so far are roughly as follows:

1. Chromosomal abnormalities

Chromosomal abnormality is one of the main causes of miscarriage. Chromosomal abnormalities include quantitative abnormalities and structural abnormalities. If one of the couple has a chromosomal abnormality, it can be passed on to the offspring, leading to miscarriage or recurrent miscarriage.

2. Maternal factors

(1) Endocrine abnormalities such as luteal insufficiency, hypothyroidism, uncontrolled diabetes, etc. (2) Systemic diseases: High fever during systemic infection can induce uterine contraction and cause miscarriage; certain known pathogen infections such as toxoplasma, cytomegalovirus, rubella virus, herpes simplex, ureaplasma urealyticum, etc. are related to miscarriage; ischemic and hypoxic diseases such as heart failure, severe anemia, hypertension, chronic nephritis and severe malnutrition in pregnant women can also lead to miscarriage. (3) Immune dysfunction, such as those with negative blocking antibodies. (4) Trauma such as squeezing the abdomen or rapid impact. (5) Bad habits such as smoking, alcoholism, excessive coffee drinking, etc. (6) Adverse factors in the environment such as harmful chemicals such as formaldehyde, benzene, lead, etc. (7) Uterine defects such as congenital uterine malformations and uterine fibroids. (8) Severe malnutrition (9) Emotional trauma such as excessive excitement, fear, sadness, anger, etc.

So, in what cases can the fetus be preserved? Generally speaking, as long as there is no direct evidence that the fetus has chromosomal problems or has been invaded by pathogenic microorganisms and deformed, the fetus should be actively preserved. Because at present, most threatened abortions are still caused by endocrine insufficiency, that is, luteal insufficiency, so the use of progesterone for active fetal preservation is very reasonable and necessary.

At this point, some people may ask, is there a method to determine early whether the fetus has genetic defects? The answer is yes, such as chorionic villus sampling (applicable before 14 weeks of pregnancy) and amniocentesis (applicable to 17-23 weeks of pregnancy), to obtain fetal chorionic villus cells or amniotic fluid cells for chromosome examination, but this test can only detect the number and structural abnormalities of the fetal chromosomes, and it is powerless for certain genetic diseases. This is its limitation, and this method is invasive. One of its disadvantages is that it artificially increases the probability of miscarriage. Another method is non-invasive genetic testing, which is based on the detection of abnormal number of stains, and cannot detect abnormalities in chromosome structure or genetic diseases. Therefore, its detection range is smaller than chorionic villus sampling and amniocentesis.

Currently, the measures used to screen for fetal chromosomal abnormalities include fetal NT examination and Down syndrome screening. Fetal NT examination indirectly provides possible evidence of fetal chromosomal abnormalities by measuring the thickness of the fetal nuchal translucency and the length of the nasal bone through B-ultrasound. The best time for the examination is 12-14 weeks of pregnancy. Although this examination has a certain auxiliary diagnostic value in indicating fetal chromosomal abnormalities, it is not absolute.

Down syndrome screening is suitable for singleton pregnant women at 16-20 weeks of gestation. It causes a high false positive rate, so it is necessary to combine fetal NT examination to comprehensively determine the risk of fetal chromosomal abnormalities.

Generally speaking, to determine whether the fetus has genetic defects, the non-invasive method should be followed first, followed by the invasive method, because the latter will artificially increase the probability of miscarriage. If it is determined that the fetus has chromosomal abnormalities or B-ultrasound indicates that the fetus has serious structural abnormalities, the pregnancy should be terminated as soon as possible. For those who plan to undergo amniocentesis directly due to advanced age or other high-risk factors, there is no need to do Down syndrome screening at this time, but the fetal NT test is still necessary, because ultrasound can also rule out fetal structural abnormalities at an early stage.