Ultrasonography
Purpose
To establish pregnancy with fetal heart motion as early as 5 to 6 weeks’ gestation
To determine an accurate expected date of birth at 20 to 22 weeks’ gestation
To determine ectopic pregnancy
To locate pockets of amniotic fluid for amniocentesis or biophysical profile
To evaluate abnormal pregnancy
To diagnose fetal abnormalities and placental location
To visualize retained products of conception
To evaluate adnexal diseases, such as tubo-ovarian abscess, hydrosalpinx, and ovarian masses
To evaluate the uterine lining (in cases of dysfunctional uterine bleeding and postmenopausal bleeding)
To monitor follicular growth during infertility treatment
To assess for Down syndrome and other chromosomal abnormalities as well as major congenital heart problems (see Nuchal translucency test)
Patient preparation
Make sure the patient has signed an appropriate consent form.
Note and report allergies.
Instruct the patient to drink fluids and avoid urination before the test because pelvic ultrasonography requires a full bladder as a landmark to define pelvic organs.
Explain to the patient that the test won’t harm the fetus.
Procedure
With the patient in a supine position (or left lateral tilt position in third trimester), coat the lower abdomen with a water-soluble conductive gel to increase sound wave conduction.
As the transducer crystal is guided over the area, images are observed on the scope and photographed.
Postprocedure care
Allow the patient to empty her bladder immediately after the test.
Remove ultrasound gel from the patient’s skin.
Normal results
During pregnancy, gestational sac and fetus are of normal size for date; placenta is located in the fundus of the uterus.
Nuchal translucency test
A nuchal translucency test helps assess the fetus for Down syndrome and some other chromosomal abnormalities as well as major congenital heart problems. It uses ultrasound to measure the translucent space in the tissue at the base of the fetal neck. Fetuses with chromosomal abnormalities tend to develop more fluid in the tissue at the base of the neck during the first trimester than fetuses without chromosomal abnormalities.
The nuchal translucency test must be performed between 11 and 14 weeks gestation. This test isn’t diagnostic for chromosomal abnormalities but only assesses risk. It should be followed by chorionic villus sampling or amniocentesis.
Abnormal results
Abnormal results may indicate fetal abnormalities, such as structural defects (spina bifida), congenital heart defects, or cleft lip and cleft palate.
Laboratory values for pregnant and nonpregnant patients
| Pregnant | Nonpregnant | |
|---|---|---|
| Hemoglobin | 11.5 to 14 g/dl | 12 to 16 g/dl |
| Hematocrit | 32% to 42% | 37% to 47% |
| White blood cells | 5,000 to 15,000/μl | 4,500 to 10,000/μl |
| Neutrophils | 60% ± 10% | 60% |
| Lymphocytes | 15% to 40% | 38% to 46% |
| Platelets | 150,000 to 350,000/μl | 150,000 to 350,000/μl |
| Serum calcium | 7.8 to 9.3 mg/dl | 8.4 to 10.2 mg/dl |
| Serum sodium | Increased retention | 136 to 146 mmol/L |
| Serum chloride | Slight elevation | 98 to 106 mmol/L |
| Serum iron | 65 to 120 mcg/dl | 75 to 150 mcg/dl |
| Fibrinogen | 400 mg/dl | 250 mg/dl |
| Red blood cells | 1,500 to 1,900/μl | 1,600/μl |
| Fasting blood glucose | 65 mg/dl | 70 to 80 mg/dl |
| 2-hour postprandial blood glucose | < 140 mg/dl (after a 100-g carbohydrate meal) | 60 to 110 mg/dl |
| Blood urea nitrogen | Decreased | 20 to 25 mg/dl |
| Serum creatinine | Decreased | 0.5 mg/dl to 1.1 mg/dl |
| Renal plasma flow | Increased by 25% | 490 to 700 ml/minute |
| Glomerular filtration rate | Increased by 50% to 160 to 198 ml/minute | 105 to 132 ml/minute |
| Serum uric acid | Decreased | 2 to 6.6 mg/dl |
| Erythrocyte sedimentation rate | 30 to 90 mm/hour | 20 mm/hour |
| Prothrombin time | Decreased slightly | 60 to 70 seconds |
| Partial thromboplastin time | Decreased slightly during pregnancy and again during second and third stages of labor (indicating clotting at placental site) | 12 to 14 seconds |
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