First Trimester Pregnancy

Chapter 13. First Trimester Pregnancy



Patient Preparation






• Preparation is similar to that for the female pelvis; however, an extremely full bladder may compress the gestational sac. Alternative: no preparation, TA imaging followed by EV imaging may be done.


Equipment and Technical Factors






• MI and TI settings must comply with the ALARA principle; pulsed-wave Doppler imaging should not be used during the first trimester to obtain an EHR because of the high intensity than can be focused on the developing heart.


• If there is difficulty locating the embryonic heart with 2D imaging, color or power Doppler imaging may be used sparingly to locate the heart for M-mode cursor placement.


• Doppler imaging may be used in the evaluation of adnexal pathologic conditions.


Imaging Protocol




Measurements



Gestational Sac






• Calculate the MSD (L + W + D)/3; correlate with patient’s dates; accuracy is +1 week.


CRL




Yolk sac






• Maximum diameter: 5.0-6.0 cm


Nuchal translucency at 9–13 weeks (45.0 mm–84.0 mm CRL)






• <3.0 mm


• MSD and CRL measurements can be referenced to standard charts and recorded on a technical worksheet if software package is not available.


• The location and size of a uterine fibroid should be documented during each sonogram of the pregnancy.



































First Trimester
Sonographic Finding(s) Clinical Presentation Differential Diagnosis Next Step



No yolk sac noted in a gestational sac >10.0 mm (EV scanning)


No embryo noted in a gestational sac >18.0 mm (EV scanning)


Irregular sac with lack of decidual reaction


Sac is low in uterus



Pregnancy “feels different”; diminished morning sickness and breast tenderness


Vaginal bleeding


Cramping


Advanced maternal age


Diabetes


History of recurrent abortions


Labs: positive β-hCG



Anembryonic pregnancy (blighted ovum)


Normal intrauterine pregnancy


Pseudosac (ectopic pregnancy)



Serial β-hCG and sonograms may be done


May require surgical intervention to resolve
Yolk sac measures >6.0 cm with/without presence of embryo Asymptomatic Enlarged yolk sac Associated with pregnancy loss



Ovarian cyst, <4.0 cm with thick walls and internal echoes


Increased flow noted with color Doppler imaging



Asymptomatic


Hemorrhage may cause pain


Labs: increased progesterone
Corpus luteum cyst


Should not persist after 16 weeks’ gestation


May need serial scans to follow regression
Cystic area in posterior fetal brain noted at 8–11 weeks’ gestation Asymptomatic Normal rhombencephalon (hindbrain) Precursor to fourth ventricle
Protrusion or bulge at umbilical cord insertion into embryo/fetus noted at 8–12 weeks’ gestation Asymptomatic
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