Diagnostic ultrasound ( PDFDrive )

1062 PART IV Obstetric and Fetal Sonography
Crown-Rump Length
Once the embryonic pole is visualized (just before 6 weeks),
measurement of the CRL of the embryo is considered the most
accurate method to date the pregnancy. 57,58
EARLY PREGNANCY FAILURE
One of the most important roles of ultrasound in the irst trimester
is to identify early pregnancies that have failed or that
are more likely to fail. Studies have demonstrated a 20% to 31%
rate of early pregnancy loss ater implantation in normal healthy
volunteers. 59,60 Many pregnancies abort before the pregnancy is
conirmed by either ultrasound or a chemical pregnancy test.
Approximately 50% of miscarriage is caused by chromosomal
abnormalities. 61 Early pathologic studies of Hertig and Rock, 60
also showed a high frequency of morphologic abnormalities
in preimplantation embryos. Loss rates are increased with
increased maternal age and prior history of early pregnancy
failure. 62
Although the etiology of irst-trimester pregnancy loss is still
not fully understood, there are many known and suspected causes.
In a study of 232 irst-trimester patients (normal, healthy women,
positive urinary pregnancy test, and no vaginal bleeding) with
TVS at the irst visit, Goldstein 57 determined the incidence of
subsequent pregnancy loss by following all to delivery or spontaneous
abortion. his group had an overall pregnancy loss rate of
11.5% in the embryonic period, (i.e., <70 days from last menstrual
period). he loss rate diminished as the pregnancy progressed.
he loss rate was 8.5% when a yolk sac was seen, 7.2% with an
embryo of CRL less than 5 mm, 3.3% with CRL 6 to 10 mm,
and 0.5% with CRL greater than 10 mm. he loss rate leveled
of at 2% from 14 to 20 weeks. herefore under the best circumstances,
the pregnancy loss rate will be 11.5% overall, from 5
weeks onward. Once the embryo reaches a CRL of 10 mm, there
is about a 98% chance of a successful outcome. Westin et al.
conirmed that ater 12 weeks menstrual age, the miscarriage
rate decreases to 0.5% in low-risk women. 63
A patient who is in the process of a spontaneous abortion
will oten present with brownish spotting, a decrease in the
symptoms of pregnancy (breast tenderness, nausea), and on
examination, a uterus smaller than expected. he latter sign is
subjective and not reliable in early gestation. Bleeding is a common
complication in early pregnancy, afecting approximately 25%
of women with documented pregnancies. 42 Women who present
with bleeding have a much higher incidence of pregnancy loss.
In women who present with a closed cervical os and uterine
bleeding in the irst trimester, 50% will eventually abort. Using
TVS, Falco et al. 64 studied 270 patients with irst-trimester bleeding
at 5 to 12 weeks’ gestation; 45% were diagnosed initially as a
nonviable pregnancy or empty gestational sac. Of the remaining
singletons with demonstrable fetal cardiac activity, 15% (23/149)
subsequently aborted. In a later prospective study of 50 patients
with MSD of 16 mm or less, no embryo, and irst-trimester
bleeding, Falco et al. 65 found that 64% eventually miscarried;
13/18 (72%) of those who continued to delivery had a yolk sac
seen; and 13/32 (40%) went on to fail even though a yolk sac
was present. Advanced maternal age (>35) and low serum β-hCG
(<1200 mIU/mL IRP) were associated with increased risk of
pregnancy failure.
Table 30.1 summarizes the rate of spontaneous abortion in
women with and without bleeding in early pregnancy. 57,64,66,67
One theorized cause of early pregnancy failure is chromosomal
anomaly in the early embryo. Sorokin et al. 68 performed chorionic
villous sampling in 795 irst-trimester pregnancies and found
that 35 had a nonviable pregnancy before the procedure; 19 of
the 35 women had subsequent chorionic villous sampling, and
all were aneuploid. Ten cases had chromosomal abnormalities,
virtually always lethal in the embryonic period, and nine had
defects with moderate potential for viability. Gestations with
low viability potential had a larger discrepancy (23.4 ± 8.3 days)
in estimated minus observed gestational age, which was signiicantly
greater than that of gestations with moderate viability
potential (8.9 ± 4.3 days; P < .001). he absence of an embryonic
pole was more common in the irst group. his demonstrates
that the more severe the anomaly is, the more likely that very
early embryonic demise or intrauterine growth restriction will
occur.
Another cause of early pregnancy failure is luteal phase defect,
thought to be failure of the corpus luteum to support the conceptus
adequately once implantation has occurred. his may result from
a shortened luteal phase in cases of ovulation induction and in
vitro fertilization (IVF), or from luteal dysfunction, more frequently
seen in obese women or women older than 37 years of
age. 69 Luteal phase defect has been deined as a delay of more
than 2 days in histologic development of the endometrium relative
to the day of the cycle. he underlying cause may be decreased
hormone production by the corpus luteum, decreased levels of
TABLE 30.1 Rate of Spontaneous Abortion in Early Pregnancy
Study Age (Wk) Number Indication Abortion Rate (%)
Goldstein 57 5-10 232 Routine 11.5
Pandya et al. 66 10-13 17,870 Routine 2.8
Stabile et al. 67 5-16 624 Bleeding 45
Falco et al. 64 5-12 270 Bleeding 51.5
Falco et al. 64 5-12 149 Bleeding + live embryo/fetus 15
Pandya et al. 66 10-13 17,870 Bleeding 15.6