The gravid uterus displaces abdominal organs cephalad and brings adnexal structures into the abdomen, which may change traditional presentations of surgical disease.

Displacement of the diaphragm reduces functional residual capacity and residual lung volume, prompting an increase in tidal volume and a physiologic respiratory alkalosis.

Uterine compression of the inferior vena cava (IVC) decreases venous return and may cause supine hypotension. This can often be mitigated by placement of the patient in left lateral tilt position to take pressure off the IVC.

Increased plasma volume, decreased hematocrit, and generally lower blood pressure make acute blood loss assessment more difficult.

The hypoalbuminemia of pregnancy predisposes the patient to edema and third spacing of fluids.

Pregnancy should not preclude any indicated surgery, regardless of trimester.

The decision for surgery must balance the risk to the fetus versus the risk to the mother for delay in intervention and should be considered with a multidisciplinary approach.

The second trimester is generally considered the preferred period during pregnancy in which to perform nonobstetric surgery. At this time, fetal organogenesis is complete, and the gravid uterus is less likely to require manipulation or obstruct the operative field.

Historically, there have been concerns regarding nonobstetric surgery performed in the first trimester due to risk of miscarriage, and surgery performed in the third trimester for risk of preterm labor. Recent examination of existing data casts doubt on whether nonobstetric surgery inherently carries risk of these obstetric complications or whether the presence of surgical disease itself, along with delays in otherwise indicated surgical intervention, is the main driver of this risk.

Ultrasonography and magnetic resonance imaging (MRI) are not associated with fetal harm and generally should be considered as first-line imaging modalities in the pregnant patient.

Gadolinium-based contrast for use with MRI is water-soluble and therefore can cross the placenta and into fetal circulation, raising the potential for teratogenicity. There is no consistent evidence of harm in human studies. However, given theoretical concerns, gadolinium should only be used when its use for a diagnostic study clearly outweighs these potential risks.

The amount of ionizing radiation that is considered to have clinically significant teratogenic or deleterious effects of the developing fetus is in the range of 5 to 10 rads (50-100 mGy). Radiation exposure via x-ray, computerized tomography (CT) scan, and nuclear medicine studies is, with rare exceptions, under this threshold, and therefore considered safe in pregnancy. See Table 23-1 for estimated fetal radiation exposure from various diagnostic imaging techniques.

Risks to the fetus from radiation exposure above the aforementioned threshold (50 mGy) include growth restriction, microcephaly, and intellectual disability; the risk is greatest during organogenesis (2-8 wk) and lessens with increasing gestational age.

Oral iodinated contrast agents are safe in pregnancy. There is theoretical concern regarding use of intravenous iodinated contrast agents that can cross the placenta to fetal circulation, although animal studies have not demonstrated teratogenic or otherwise adverse effects. Therefore, if intravenous contrast is necessary for a particular diagnostic study, the benefits generally outweigh these theoretical risks.

Breastfeeding may be continued without interruption after use of either iodinated or gadolinium-based contrast.

Typical anesthetic agents used in standard concentrations for local, regional, and general anesthesia, including sedatives, analgesics, and paralytics, are safe for use in pregnancy.

Blood pressure support in the normotensive range is critical intraoperatively to maintain perfusion to the fetus.

Oxygen saturation should be maintained greater than 95% in the pregnant patient.

When possible, a preoperative fluid bolus should be used to guard against a hypotensive episode following an epidural test bolus.

Laparoscopy can be undertaken safely during pregnancy, even at advanced gestational age, and often is the preferred modality for management of a variety of surgical diseases in the pregnant patient.

Access may be gained with the open (Hasson), closed (Veress needle), or direct optical trocar techniques; however, care must to be taken to note the height of the uterine fundus and adjust entry point and trocar placement accordingly.

Ultrasound-guided entry has been described as a technique and may be used to reduce the risk of uterine injury.

Despite historical concerns regarding carbon dioxide and association with fetal toxicity in animal studies, there is no evidence to suggest such harm in humans.

Insufflation pressures of 10 to 15 mm Hg are recommended for the pregnant patient.

The extent of fetal monitoring recommended depends on the gestational age and viability of the fetus, the type of anesthesia being administered, and the nature and acuity of the surgical intervention

At minimum, fetal status should be documented prior to and after surgery: For a previable fetus less than 23 to 24 weeks, a fetal heart rate is sufficient.

Continuous intraoperative fetal monitoring may be considered when the following criteria are met: logistically able to use an external monitor without interfering with the surgery or sterile field, staff is available to interpret the results, and a physician is available to intervene if indicated.

A nonreassuring fetal heart tracing intraoperatively can often be improved by identifying and correcting maternal hypotension and/or maternal hypoxia; it does not necessarily require urgent cesarean delivery.