Spontaneous Abortion Laboratory Findings
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A. Complete Blood Count
If significant bleeding has occurred, the patient will be anemic. Both the white blood cell count and the sedimentation rate may be elevated even without the presence of infection.
B. Pregnancy Tests
Falling or abnormally low plasma levels of β-hCG are predictive of an abnormal pregnancy, either a blighted ovum, spontaneous abortion, or ectopic pregnancy.
Ultrasonography
Transvaginal ultrasound is helpful in documenting intrauterine pregnancies as early as 4-5 weeks’ gestation. Fetal heart motion should be seen in embryos > 5 mm from crown to rump, or in embryos at least 5-6 weeks’ gestation. Ultrasound is useful in determining which pregnancies are viable and which are most likely to miscarry. Perhaps more than any other tool, ultrasound has proven most helpful in the differential diagnosis of early pregnancy complications.
In threatened abortion, ultrasound will reveal a normal gestational sac and viable embryo. However, a large or irregular sac, an eccentric fetal pole, the presence of a large (> 25% of sac size) retrochorionic bleed, and/or a slow fetal heart rate (< 85 bpm) carry a poor prognosis. Miscarriage becomes less and less likely the further the gestation progresses, but most pregnancies are lost weeks before mothers complain of signs or symptoms. If a viable fetus of 6 weeks or less is seen on ultrasound, the risk of miscarriage is approximately 15-30%. This decreases to 5-10% at 7-9 weeks’ gestation and less than 5% after 9 weeks’ gestation.
In incomplete abortion, the gestational sac is usually deflated, and irregular, echogenic material representing placental tissue is seen in the uterine cavity. In complete abortion, the endometrium appears closely apposed, with no visible products of conception.
An embryo or fetus without heart motion is consistent with a missed abortion, while an abnormal gestational sac, without a yolk sac or embryo, is consistent with a blighted ovum (see Figs 14-3, 14-4, 14-5 and 14-6).
Ectopic pregnancy may cause similar symptoms of miscarriage, namely menstrual abnormality and abdominal or pelvic pain. An adnexal mass may or may not be present. Ultrasound can virtually exclude an ectopic pregnancy by documenting an intrauterine pregnancy, as the chance of a simultaneous intra- and extrauterine pregnancy (heterotopic pregnancy) is exceedingly rare in spontaneous pregnancies, occurring in only one in 15,000-40,000 pregnancies.
Hydatidiform mole usually ends in abortion before the fifth month. Theca lutein cysts, when present, cause bilateral ovarian enlargement; the uterus may be unusually large. Bloody discharge may contain hydropic villi.
Other entities that may be confused with abortion include cervical infection, extruding pedunculated myoma, and cervical neoplasia. However, the pregnancy test will be negative, unless a pregnancy coexists.
Revision date: July 5, 2011
Last revised: by Jorge P. Ribeiro, MD
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