What is a chemical miscarriage? Types and causes of miscarriage【supervised by doctor】

Introduction

Miscarriage is a condition in which the foetus dies early in pregnancy after the pregnancy is confirmed. Miscarriage is defined as ‘termination of pregnancy less than 22 weeks’, with less than 12 weeks’ gestation being referred to as ‘early miscarriage’ and from 12 to 22 weeks’ gestation as ‘late miscarriage’.

There are different types of miscarriage, including chemical, imminent and comorbid miscarriages, each with different symptoms and treatment. The probability of miscarriage also increases with maternal age, with about half of pregnant women over the age of 40 suffering a miscarriage.

What is a chemical miscarriage (chemical abortion)?

A chemical miscarriage (chemical abortion) is a condition in which a pregnancy test is positive, but no foetal sac can be seen in the uterus. Chemical miscarriage is sometimes referred to as chemical miscarriage, chemical pregnancy or biochemical pregnancy, both of which are considered synonyms.

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In Japan, a chemical abortion is defined as a miscarriage that is not included in the number of miscarriages, and is different from a clinical miscarriage after an ultrasound examination (ultrasound examination) confirms the presence of a foetal sac in the uterus.

Chemical abortion (chemical abortion/chemical pregnancy/biochemical pregnancy)

A condition in which hCG (human chorionic gonadotropin) is detected and positive in urine or blood, but no foetal sac is seen on ultrasound and the pregnancy is terminated and hCG is negative.

Clinical pregnancy

The presence of a foetal sac in the uterus on ultrasound examination.

Clinical abortion

A condition in which the foetus dies for some reason after an ultrasound examination reveals a foetal sac in the uterus.

Differences from an imminent miscarriage

An imminent miscarriage occurs when the pregnancy is less than 22 weeks and, as the word ‘imminent’ indicates, the miscarriage is imminent. In many cases, the foetus remains alive (and survives) in the womb despite abdominal pain and bleeding. For these reasons, it can be said that an imminent miscarriage differs from a chemical miscarriage in that there is a possibility of continuing the pregnancy.

Other types of miscarriage

Progressive miscarriage

A condition in which the contents of the uterus are ejected from the body with bleeding. There are two types of miscarriage: complete miscarriage, in which all the uterine contents have been expelled, and incomplete miscarriage, in which some of the uterine contents remain in the uterus. In both cases, miscarriage surgery is considered depending on the symptoms.

Abortive abortion

A condition in which the foetus remains in the uterus, although the foetal sac has not developed or the foetus is confirmed dead. The mother has few symptoms and in some cases the miscarriage is detected on examination. A retained miscarriage can be expelled spontaneously or, depending on the number of weeks and the condition, a miscarriage operation can be performed to remove the uterine contents.

Miscarriage due to infection

In some cases, sexually transmitted diseases such as chlamydia, syphilis and herpes, and foetal infection with hepatitis B and cytomegalovirus cause severe conditions or foetal death in mother and foetus.

Probability of chemical abortion

Pregnancy is defined as the identification of a foetal sac in the uterus or an ectopic pregnancy (ectopic pregnancy). For these reasons, a chemical miscarriage is defined as neither being counted as a number of pregnancies nor as a number of miscarriages.

Many people consider a chemical miscarriage to be a menstruation or irregular bleeding if they are not aware of a pregnancy. Therefore, it can be said that the exact probability of a chemical miscarriage is not known.

Symptoms of chemical abortion

Chemical miscarriages often have no symptoms and are considered by many to be menstruation. The amount of bleeding caused by a chemical miscarriage is considered to be about the same or slightly more than a normal period. In rare cases, liver-like jelly-like clots of blood may be discharged, but these are secretions from the uterus and are not the embryo.

If you wish to become pregnant or have a baby and a positive pregnancy test shows bleeding, see an obstetrician/gynecologist as soon as possible.

Signs of chemical abortion

If the miscarriage is a chemical miscarriage, the diagnosis is made at around 4-5 weeks’ gestation, when the first ultrasound scan is performed. A chemical miscarriage is a miscarriage that occurs very early in the pregnancy. The nausea, breast and abdominal distension that usually occur in pregnancy are not present, and the signs of a chemical miscarriage are almost non-existent.

Chemical miscarriage and basal body temperature

A woman’s basal body temperature has a high temperature phase before menstruation due to the secretion of luteinising hormone (progesterone), and then enters a hypothermic phase with a decrease in the secretion of luteinising hormone (progesterone) at the start of menstruation.

However, pregnancy causes the secretion of luteinising hormone (progesterone) to continue and the basal body temperature does not fall even after the expected menstrual period has passed. For these reasons, if hypothermia persists after a positive pregnancy test, there is a high possibility of a chemical miscarriage.

Causes of chemical abortion

The causes of chemical abortion are still unknown. However, many miscarriages in early pregnancy are due to chromosomal abnormalities in the foetus, and it is believed that chemical miscarriage may also be affected by chromosomal abnormalities.

Chemical miscarriages can occur in both natural and IVF pregnancies and are more common in women with older pregnancies over 35 years of age.

Differences between chemical abortion and ectopic pregnancy

Ectopic pregnancy, like chemical abortion, is a condition in which a pregnancy test is positive but no foetal sac is seen on ultrasound examination. An ectopic pregnancy, also known as an ectopic pregnancy, is a condition in which a fertilised egg implants in an area outside the uterus, such as the fallopian tubes.

The fertilised egg cannot develop outside the uterus, making continued pregnancy impossible. In addition, ectopic pregnancies may have no symptoms and can lead to rupture of the fallopian tubes due to the enlargement of the embryo and the foetal sac. Unlike chemical abortion, ectopic pregnancy is often life-threatening for the mother.

For these reasons, it is important to seek medical attention at an obstetrician and gynaecologist whenever a positive pregnancy test is detected.

If diagnosed with a chemical miscarriage

Chemical miscarriages can occur in both natural and IVF pregnancies. Among the most common miscarriages occur in pregnant women over 35 years of age, who are considered to have an older childbirth. However, the risk of both types of miscarriage increases with maternal age, so caution should be exercised if you are planning to conceive or give birth in your 30s or later.

After a chemical miscarriage

After a chemical miscarriage, the fertilised egg that did not continue the pregnancy is expelled with bleeding. For this reason, many pregnant women who do not use a pregnancy test often consider a chemical miscarriage to be a menstrual period and do not realise that they have had a miscarriage.

A chemical miscarriage is the loss of a fertilised egg. It is a natural expulsion with bleeding and therefore does not require treatment if there are no abnormalities.

How long is a pregnancy test positive?

Many pregnant women are so concerned about chemical miscarriage that they repeatedly use pregnancy tests to confirm a positive result. Once a positive pregnancy test is confirmed, the pregnancy test will still give a negative result if a chemical miscarriage occurs.

Pregnancy after chemical abortion

If a chemical miscarriage occurs, the effect on subsequent pregnancies is considered to be minimal. It can be said that after a chemical miscarriage, the woman returns to a fertile state with the arrival of her next menstrual period.

However, it is important to note that the risk of miscarriage increases with increasing maternal age and smoking behaviour, including second-hand smoke.

Female infertility

Infertility is a condition in which a woman is unable to have a baby due to repeated miscarriages and stillbirths after conception. Two previous miscarriages are referred to as repeated miscarriages and three or more as habitual miscarriages. Most cases of infertility are also considered to be due to chromosomal abnormalities in the foetus.

However, even if a woman is diagnosed with miscarriage-prone infertility, the chances of conception are high and if no abnormalities of uterine morphology are detected, the prognosis for the next pregnancy is said to be relatively good.

What is NIPT for early knowledge of the risk of miscarriage?

There are many different types of miscarriage other than chemical miscarriage, and all causes of miscarriage are still unknown. However, many miscarriages are believed to be caused by chromosomal abnormalities in the foetus. For these reasons, it is important to know the risk of miscarriage at an early stage in order to have a healthy pregnancy.

NIPT by Hiro Clinic NIPT is a screening test that can be performed as soon as the pregnancy is confirmed by an ultrasound scan. It is performed by drawing blood from the mother’s arm only, so there is no direct invasion (damage) to the foetus.

NIPT is considered to be extremely accurate compared to conventional blood-based prenatal diagnosis, with a sensitivity and specificity of 99.9% for Down syndrome (21 trisomy), Edwards syndrome (18 trisomy), Patau syndrome (13 trisomy).

If you have any questions or concerns about the risk of miscarriage due to chromosomal abnormalities in the foetus or about NIPT, please contact Hiro Clinic NIPT for a detailed explanation by doctors and staff who are familiar with NIPT.

Article Editorial Supervisor

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Dr Hiroshi Oka

NIPT specialist clinic, MD

Graduated from Keio University, School of Medicine