DIAGNOSIS OF PREGNANCY
Findings on examination
The endocrinological, physiological, and anatomical alterations that accompany pregnancy give rise to symptoms and signs classified into three groups that provide evidence that pregnancy exists;
Symptoms of Pregnancy
History of sexual contact or Artificial Insemination by Donor (AID) or Husband (AIH)
Nausea with or without vomiting – Begins about 6 weeks after the commencement (first day) of the last menstrual period, and ordinarily disappears spontaneously 6-12 weeks later. The cause of this disorder is unknown but seems to be associated with higher levels of selected forms of hCG with the greatest thyroid-stimulating capacity.
Disturbances in Urination – During the first trimester, the enlarging uterus, by exerting pressure on the urinary bladder, may cause frequent micturition but as pregnancy progresses, the frequency of urination gradually diminishes as the uterus rises up into the abdomen. The symptom of frequent urination reappears near the end of pregnancy, however, when the fetal head descends into the maternal pelvis (engagement), impinging upon the volume capacity of the bladder.
Perception of Fetal Movement – Between 16-18wks (menstrual age) in multigravida and 18-20wks in primigravida, the pregnant woman becomes conscious of slight fluttering movements in the abdomen caused by fetal movements, and the day that these are first recognized by the pregnant woman is designated as quickening, or the perception of life and is a milestone of the progress of pregnancy that can help to establish the duration of gestation.
2. Signs of Pregnancy
Cessation of Menses – It is not until 10 days or more after the time of expected onset of the menstrual period, therefore, that the absence of menses is a reliable indication of pregnancy. When a second menstrual period is missed, the probability of pregnancy is much greater.
Conception may occur without prior menstruation, that is, in a girl before menarche.
Nursing mothers, who usually sustain amenorrhea during lactation because of lactation-induced hypogonadism and anovulation, sometimes ovulate and conceive at that time.
More rarely, women who believe they have passed the menopause may ovulate again after a few months of anovulation/amenorrhea and become pregnant.
Brief and scant uterine bleeding as a consequence of blastocyst implantation somewhat suggestive of menstruation occurs occasionally after conception.
One or two episodes of bloody discharge, somewhat reminiscent of and sometimes misinterpreted as menstruation, are not uncommon during the first half of pregnancy.
Bleeding per vagina at any time during pregnancy must be regarded as abnormal and portends an increased likelihood of serious pregnancy complications.
DDx – Anovulation secondary to: severe illness physiological aberrations induced by emotional disorders, including the fear of pregnancy, environmental changes.
Cervical Mucus – If cervical mucus is aspirated, spread on a glass slide, allowed to dry for a few minutes, and examined microscopically, characteristic patterns can be discerned that are dependent on the;
Stage of the ovarian cycle
Presence or absence of pregnancy, that is, on progesterone secretion in large amounts
From about the 7th-18th day of the menstrual cycle, a fern-like pattern/process of arborization/palm leaf pattern of dried cervical mucus is seen due to crystallization of the mucus.
After the 21st day, a beaded or cellular appearance forms that is also encountered in pregnancy due to progesterone production.
Changes in the Breasts
– Prolactin-secreting pituitary tumors
Drugs e.g. benzodiazipines, which induce hyperprolactinemia
Spurious or imaginary pregnancy
Discoloration of the Vaginal Mucosa – During pregnancy, the vaginal mucosa usually appears dark bluish or purplish-red and congested; this is the so-called Chadwick sign.
DDx – intense congestion of pelvic organs
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Increased Skin Pigmentation and Appearance of Abdominal Striae
DDx – ingestion of estrogen- progestin contraceptives
Leg swelling in late pregnancy
Other maternal adaptations in pregnancy (see related notes)
PROBABLE EVIDENCE OF PREGNANCY
Enlargement of the Abdomen
Changes in Size, Shape, and Consistency of the Uterus
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Average uterine diameter at 12 weeks – 8 cm
Hegar sign positive by 6-8wks – DDx – when the walls of the uterus of a nonpregnant woman are excessively soft-adnexa uteri
Changes in the Cervix – By 6-8 weeks, the cervix usually is considerably softened. In primi gravidas, the consistency of cervical tissue that surrounds the external os is more similar to that of the lips of the mouth than to that of the nasal cartilage, which is characteristic of the cervix in nonpregnant
DDx – estrogen- progestin contraceptives
-The cervix may remain firm during pregnancy in certain inflammatory conditions, as well as with carcinoma.
Braxton Hicks Contractions – During pregnancy, the uterus undergoes palpable but ordinarily painless contractions at irregular intervals from the early stages of gestation.
DDx – hematometra (collection or retention of blood in the uterine cavity)
-Pedunculated, submucous myomas
Ballottement – Near midpregnancy, the volume of the fetus is small compared with that of amnionic fluid. Consequently, sudden pressure exerted on the uterus may cause the fetus to sink in the amnionic fluid and then rebound to its original position; the tap produced (ballottement) is felt by the examining fingers.
Outlining the Fetus
DDx – subserous myomas
Hormonal Tests of Pregnancy – The presence of human chorionic gonadotropin (hCG) in maternal plasma and its excretion in urine provides the basis for the endocrine tests for pregnancy.
POSITIVE SIGNS OF PREGNANCY/ESTIMATION OF FETAL MATURITY
The three positive signs of pregnancy and estimating fetal maturity are;
Identification of Fetal Heart Action
Contractions of the fetal heart can be identified by;
– auscultation with a Pinard fetoscope – The fetal heartbeat can be detected 16-18 weeks, on average in thin women, and by 22-24weeks in nearly all other pregnancies in non obese women and in the absence of hydramnios.
– Doppler principle with ultrasound at 6 weeks
– U/S at 4-5 weeks at the same time the fetal pole is visible
Fetal heart rate
120-160 beats per minute and is heard as a double sound resembling the tick of a watch under a pillow.
Other sounds heard on abdominal auscultation;
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– The Funic/Fetal/Funicular/Umbilical soufflé – a sharp, whistling sound caused by the rush of blood through the umbilical arteries. It is that is synchronous with the fetal heart beat, sometimes only systolic and sometimes continuous, heard on auscultation over the pregnant uterus
– The Uterine/Placental soufflé – a soft, blowing sound produced by the passage of blood through the dilated uterine vessels that is synchronous with the maternal pulse heard most distinctly during auscultation of the lower portion of the uterus from 16 wks onwards.
DDx – Increased blood flow to the uterus in; – large uterine myomas, large ovarian tumors
– The sounds resulting from movement of the fetus
– Maternal pulse
-The gurgling of gas in the intestines of the pregnant woman
3.Perception of Fetal Movements(quickening) – Felt after about 20wks
IMAGE RECOGNITION OF PREGNANCY
A normal pregnancy may be demonstrated by
Abdominal pulse echo sonography after 4-5 weeks menstrual age.
After 6 weeks, the small white gestational ring is characteristically visible.
Embryonic poles can be demonstrated within the gestational ring by 7 weeks menstrual age.
Radiography (not in use) – Foci of ossification in the fetus appears at 12-14wks;
Lower femur – 36wks;
Upper tibia – 37wks
PREGNANCY TESTS – DETECTION OF CHORIONIC GONADOTROPIN
hCG is secreted by the syncytiotrophoblast to prevent the involution of the corpus luteum, the principal site of progesterone formation during the first 6 weeks of pregnancy.
hCG is a luteinizing hormone (LH)-like agent that acts as an LH surrogate in responsive tissues, such as the ovary (corpus luteum) and testis (Leydig cells). Specifically, hCG acts by way of the plasma membrane LH receptor.
The chemical detection of pregnancy involves the demonstration of hCG in blood or urine of the woman to be tested.
The tests for detecting hCG involve the principles of;
Immunoassays of hCG without Radioisotopes;
– Agglutination Inhibition – this is the prevention of flocculation of hCG-coated particles, such as latex particles to which hCG is covalently bound. The commercially available kits that employ failure of agglutination of latex particles to detect hCG in urine contain two reagents.
One is a suspension of latex particles coated with or covalently bound to hCG, and the other contains a solution of hCG antibody. To test for hCG, one drop of urine is mixed with one drop of the antibody-containing solution on a black glass slide. If hCG is not present in the test sample, antibody will remain available to agglutinate the hCG-coated latex particles, which are added subsequently. Therefore, the pregnancy test is positive if no agglutination occurs; the pregnancy test is negative when agglutination occurs. Results are ready in 2mins at 4 wks gestation.
– Enzyme-linked immunosorbent assay (ELISA)
– Time-resolved immunoflurometric assays (IFMA)
Immunoassays of hCG Using Radioisotopes
– Radioimmunoassay using antibodies directed against the -subunit of hCG (which are specific for hCG and not cross-reactive with LH cf -subunit of hCG and LH which are identical), the pregnancy hormone can be detected in maternal plasma or urine by 8-9 days after ovulation
– Immunoradiometric assay (IRMA)
Bioassays (Obsolete) – development of ovarian hyperemia in the immature rat when injected with maternal urine positive for hCG; insensitive, remarkably accurate as early as 4-5 weeks after ovulation or at least by the time of the second missed menses
DDX OF PREGNANCY(not attended by cessation of menses)
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tumors occupying the pelvis or abdomen
contiguous but extrauterine mass(es)
ESTIMATION OF FETAL MATURITY
Naegele’s rule – Subtract 3 from the month of the LNMP, and add 7 to the first day of the LNMP
Normal Pregnancy Lasts (calculated from last normal menstrual period (LNMP))
9 calendar months
10 lunar months (28 days)
Uterine size/fundal height (see notes above)
Quickening (see notes above)
Fetal heart tones (see notes above)
Fetal weight – Estimation of fetal weight is important when the physician must decide whether to;
allow delivery to proceed as a natural event
use tocolytic agents
perform cesarean section
Johnson’s formula for estimation of fetal weight in vertex presentations:
Fetal weight (gm) = fh (cm) – n x 155
n = 12 if vertex is above ischial spines
n = 11 if vertex is below ischial spines
fh = fundal height (measured from the pubic symphysis)
If the patient weighs more than 91 kg (200 lb), 1 cm is subtracted from the fundal height
Fetal Measurements (at term)- Crown-rump length
– Femur length – 7.7cm
– Biparietal diameter – 9.5cm
– Head circumference – 34.6cm
– Abdominal circumference – 35.3cm
Chorionic villus sampling – first-trimester alternative to amniocentesis
Percutaneous umbilical cord sampling
Tests for Fetal Well Being
Magnetic resonance imaging
Confirmation of fetal lung maturity
Lecithin:Sphingomyelin (L/S) Ratio – determination of the the relative concentration of surfactant-active phospholipids confirms fetal lung maturity. Before 34 weeks, lecithin and sphingomyelin are present in amnionic fluid in equal At about 34 weeks, the concentration of lecithin relative to sphingomyelin begins to rise – Lecithin:Sphingomyelin ratio of 2:1 is mature
Foam Stability (Shake) Test – The test depends upon the ability of surfactant in amnionic fluid, when mixed appropriately with ethanol, to generate stable foam at the air-liquid interface.
There are two problems with the test:
– Slight contamination of amnionic fluid, reagents, or glassware, or errors in measurement, may alter the tests results
– A false-negative test is rather common.
Diagnosis of Fetal Death
The woman, with anxiety in her voice, reports that she has not felt fetal movement for hours or for 1-2 days
The fetal heart is not heard by auscultation or identified by real-time ultrasound examination after 10-12 wks
Fetal skull – scalp edema
On palpation, the loose bones of the fetal head feel as though these are contained in a flabby bag
an enlarged amniotic cavity, compared with the crown-rump length, in early gestation
If the fetus has been dead for some time;
The uterus does not correspond in size to the estimated duration of pregnancy, or that the uterus has actually become smaller than previously observed
Maternal weight gain ceases/slight decrease in weight
Retrogressive changes in the breasts
The amniotic fluid is red to brown and usually turbid rather than nearly colorless and clear – This finding is not absolutely diagnostic of fetal death, however, because prior hemorrhage into the amniotic sac, as rarely occurs during amniocentesis, may lead to similar discoloration of the amniotic fluid even though the fetus is alive.
Radiological signs of fetal death (done late in pregnancy);
Spalding sign – Significant overlap of the skull bones, caused by liquefaction of the brain, a process that requires several days to develop. A similar sign may develop occasionally with a living fetus, as when the fetal head is compressed in the maternal pelvis.
Roberts sign – Exaggerated curvature of the fetal spine – Because this sign depends on maceration of the spinous ligaments, its development also requires several days; moreover, mild degrees of curvature of the spine in living fetuses may be misleading.
Demonstration of gas in the fetus is an uncommon but reliable sign of fetal death