The essential first step in approaching a pregnant patient with abdominal pain is to obtain a detailed history. It is also vital to establish the accurate gestational age early in the patient evaluation, as the presentation of symptoms and signs may vary with gestational age, and to plan premature delivery if necessary.
The time of onset, duration, and other characteristics of the pain should be sought:
Location: sudden-onset flank pain can indicate nephrolithiasis or pyelonephritis
Intensity and characteristics: mild, moderate, or severe; intermittent, sharp, full, or achy
Radiation: for example, abdominal pain radiating to the back may suggest cholecystitis or pancreatitis
Localisation: for example, pain in the RLQ can indicate appendicitis, ovarian torsion, or ectopic pregnancy
Acute or chronic: previous ultrasound reports should be requested.
Following vital signs, abdominal examination includes assessment of symphysis-fundal height, consistency and tenderness of the uterus, position and engagement of the presenting part, and fetal heart rate.
To differentiate between extra- and intrauterine tenderness, it is helpful to examine the patient in the right or left decubitus position by displacing the gravid uterus to one side. The location of some organs may vary according to the stage of pregnancy as the gravid uterus grows. In addition, the laxity of the anterior abdominal wall makes signs such as rebound tenderness and guarding non-specific. This is particularly pronounced in multiparae due to a decrease in abdominal wall tone.
When assessing early pregnancy conditions, such as ectopic pregnancy and miscarriage, it is essential to determine whether the pain originates from the uterus.
Pelvic examination should be preceded by speculum insertion to visualise the cervix and take vaginal and cervical swabs if necessary. Digital evaluation should focus on the presence of cervical motion tenderness and thorough assessment of the adnexa.
To assess fetal wellbeing, CTG evaluates the presence of contractions and relates them to the fetal heart rate. It is important to differentiate between maternal and fetal pulse. For the most accurate assessment, CTG speed should be appropriate. Its interpretation must take into account frequency of uterine contractions, baseline rate, accelerations, decelerations, and variability. CTG is essential in cases of placental abruption and uterine rupture. In patients affected by blunt trauma, fetal monitoring should always be instituted promptly rather than delayed until the patient reaches the antenatal area.
Abdominal/pelvic ultrasound is the initial and most frequently used imaging modality for evaluating abdominal pain in pregnancy, largely due to its safety. It allows easy assessment of maternal gallbladder, pancreas, and kidneys and can exclude pancreatitis, pyelonephritis, nephrolithiasis, and cholelithiasis. Ultrasound of the upper urinary tract is indicated in cases of unexplained abdominal or back pain during pregnancy. The presence of fluid on abdominal/pelvic ultrasound may suggest intraperitoneal haemorrhage (e.g., splenic rupture). In potentially haemodynamically unstable patients, scanning should be performed expeditiously. Ultrasound remains the principal method of assessing fetal gestational age, fetal heart activity, fetal activity, and amniotic fluid volume.
Transvaginal ultrasound is regarded as the imaging method of choice for patients who present with abdominal pain in early pregnancy, including diagnoses of miscarriage or ectopic pregnancy. It allows clear visualisation of the normally developing embryo along with other abnormalities and is useful to assess the uterus and the extra-uterine structures. Many causes of abdominal pain may be ruled out on transvaginal ultrasound, such as ovarian torsion, ovarian cysts, and degenerating fibroids.
Abdominal x-ray may be a necessary diagnostic tool in some rare cases (e.g., bowel obstruction, nephrolithiasis). Concerns about exposing the fetus to radiation should be weighed against the morbidity and mortality that may result from a delayed or missed diagnosis.
CT scan of the abdomen may be indicated in cases of severe necrotic pancreatitis or if the diagnosis of appendicitis or splenic rupture is unclear. As with plain film x-rays, such imaging techniques should only be considered if the risk of maternal morbidity and mortality outweighs the risk of fetal radiation exposure. This cautious approach has led to the development of evidence-based guidelines to support physicians in the evaluation of risks and benefits, which should always be considered and discussed with patients prior to their implementation.
MRI is expensive and time-consuming and can be uncomfortable for pregnant patients. It may be of use in defining specific characteristics of an adnexal mass or aiding the diagnosis of nephrolithiasis. More recently, MRI has been considered the preferred test after inconclusive ultrasound scan in the evaluation of RLQ pain, due to the lack of ionising radiation. However, it is not recommended during the first trimester, as the effect of MRI on fetal development is unclear.
Serum beta-hCG should be the initial test requested for all patients presenting with abdominal pain when <20 weeks pregnant. This, in combination with the use of transvaginal ultrasound, confirms or excludes the presence of an intrauterine pregnancy. FBC should also be included in the initial work up, particularly estimation of Hb, platelets, and haematocrit (if vaginal bleeding is present). Type and screen is necessary in the presence of abnormal vaginal bleeding (as may occur with ectopic pregnancy, miscarriage, uterine rupture, or placental abruption) or if there is concern regarding the possibility of an intra-abdominal/intra-peritoneal bleed (e.g., splenic rupture). If ovarian hyper-stimulation syndrome (OHSS) is suspected, additional tests indicated include a serum electrolyte panel, LFTs, and coagulation screen.
FBC (particularly estimation of Hb, platelets, and haematocrit) is the initial investigation requested for all patients presenting with abdominal pain beyond 20 weeks pregnant. Type and screen is also recommended for all patients presenting at this stage, as well as a serum electrolyte panel and LFTs (abnormalities found in haemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome, acute fatty liver of pregnancy, and acute pancreatitis). A coagulation screen is indicated as clotting abnormalities may occur in placental abruption, uterine rupture, and HELLP syndrome.
Urinalysis (macroscopic and microscopic) should be included in the baseline investigations for all pregnant patients presenting with abdominal pain throughout pregnancy. Not only is it useful to assess the presence of urinary tract abnormalities, but the detection of protein in the urine alerts the physician to the possibility of a serious underlying condition such as HELLP syndrome.
Interpretation of all these results must take into account the effects of the physiological changes of pregnancy. It is therefore worth considering that some laboratory parameters are modified because of haemodilution due to an increase in plasma volume. LFTs are affected, having the upper end of the normal range for most of its tests reduced; however, this alteration does not apply to serum alkaline phosphatase, which increases steadily throughout pregnancy. With respect to FBC and haemoglobin level, a cut-off of <110 g/L (<11 g/dL) is usually employed to diagnose ante-partum anaemia. In addition, a definition of gestational thrombocytopenia can be used to describe healthy pregnant women with a platelet count of >115 x 10^9/L in the third trimester; this threshold may be regarded as safe and not requiring further investigation. Another well-known feature of a normal pregnancy is leukocytosis, since it plays a crucial role in protecting the fetus by ascending infections.
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