Abnormalities in the First Three Months of Pregnancy

Small Gestational Sac

A small gestational sac is usually due to a blighted ovum (anembryonic gestation) and is a fairly common finding. On ultrasound examination, the gestational sac is found to be smaller than expected for the gestational age, and the fetus cannot be demonstrated.

If an early pregnancy is clinically normal, but an ultrasound scan shows an enlarged uterus, an anembryonic gestation should be suspected: repeat the examination after 7 days. If the pregnancy is normal, the sac should have grown, and the fetus and the heart activity should be clearly seen at the second examination.

Fetal death (spontaneous abortion)

When there is a fetal or embryonic death, the patient may remain clinically normal and may continue to feel pregnant for days. There may be a history of bleeding or abdominal cramp. The uterus may be normal, small, or even enlarged if there is a significant intrauterine hematoma. The fetal pole may be visible but no heart action will be demonstrated. If the examination is made during the first 8 weeks of pregnancy, it should be repeated after another 7 days. After the eighth week, fetal life should always be demonstrable in a normal pregnancy.

It should always be possible to demonstrate fetal heart activity after the eighteen weeks of pregnancy.

Empty uterus

The patient will have a history of amenorrhoea followed by loss of blood. sometimes with recognition of the fetus. If this is recent, the uterus may still be large, approximately the expected size for gestational age. The scan will show the uterus to be empty.

Incomplete abortion

The patient may have a history of amenorrhoea, followed by loss of blood; she may have seen the fetus. If this is recent, the uterus may still be large, approximately the expected size for gestational age. However, the uterus may be empty and the endometrial canal may be normal. If the abortion is incomplete, the uterus will be smaller than expected for gestational age and filled with an abnormally shaped sac or with an amorphous mass of variable size, shape, and echogenicity. This is the retained placenta and blood clots. There will be no sign of fetal life.

It can be difficult to recognize the retained products of conception after a spontaneous abortion. This diagnosis should not be made unless there are identifiable parts, such as a yolk sac, gestational sac, or dead embryo. Endometrial thickening is not a reliable way of recognizing or excluding retained products of conception, and a molar pregnancy must be excluded.

Be warned: the patient's estimate the gestational age is not always accurate.

 Large Uterus

The  commonest causes of a uterus larger than expected are:

• Hydatidiform mole.
• Choriocarcinoma.
• Intrauterine bleeding is associated with spontaneous abortion.
• Uterine myoma (fibroids).

1. Hydatidiform mole. 

Clinical findings are nonspecific. Ultrasound is almost always abnormal and shows a large uterus filled with a mass of uniform echoes providing a regular speckled appearance: the "snow-storm" effect. It may be difficult to distinguish a mole from echogenic blood within the uterus, but blood is usually more heterogeneous and less echogenic than a mole, which may have cystic spaces (vesicles). 

In older patients, in particular, a large myoma may cause confusion, but moles will have stronger back wall echoes and central necrosis. It is important to remember that the fetus may still be present and only part of the placenta may be affected. Embryos in association with moles have a high incidence of chromosomal abnormalities.

2. Choriocarcinoma may be indistinguishable from a hydatidiform mole by ultrasound, but it should be considered if the uterus is much larger than expected and the ultrasound scan shows areas of hemorrhage and necrosis rather than the uniform echoes of a mole. The pattern of choriocarcinoma may be mixed, with both solid and fluid echoes, rather than the homogeneous snow-storm effect of a mole. Rarely there may be disease elsewhere: X-ray the chest to exclude metastases.

3. Intrauterine hemorrhage due to threatened or spontaneous abortion. 

This is mainly a clinical diagnosis based on bleeding in early pregnancy: ultrasound may show a varying amount of blood in the uterus, separating the chorioamniotic membrane from the decidua (the lining of the membrane of the uterus), which shows as a clearly defined anechogenic area. The blood may be completely anechogenic or echogenic. 

It is usually heterogeneous. It is very important to search for signs of fetal life because this will influence the way the patient is managed. If there is any doubt. repeat scans at one- or two-week intervals to evaluate the progress of the pregnancy.

If there is any doubt after one scan, repeat it one or two weeks.

4. Large irregular uterus. In the first trimester a large, irregular

The uterus is usually due to uterine myomas. Record the size and position of the myomas and estimate the potential difficult ties that they may cause during labour. The myomas should be reviewed at 32-36 weeks' gestation. The central area may become necrotic, showing a mixed or echo-free pattern. This does not necessarily have any clinical significance. Amyoma can be mimicked by contraction of the uterine muscle, and the scan should be repeated after 20-30 minutes to see if the contraction area changes. Contractions are normal and indent the inner aspect of the uterus.