Problems & Answers

Anesthesia during Pregnancy

©G.M. Woerlee, 2005–2018

A pregnant woman will come into contact with trace concentrations of anesthetic gases in the air while working in an operating theater, and higher concentrations of these same drugs if she requires a surgical procedure under anesthesia during pregnancy.

Old studies aroused fears...

Early in the 1970's concern arose about the possible effects of exposure to trace concentrations of gases upon the chance of miscarrying, ectopic pregnancy, stillbirth, or giving birth to an abnormal child. Evidence for the reality of these concerns was seemingly confirmed by articles showing that:

All these general health and reproductive problems were attributed to trace concentrations of waste anesthetic gases in the operating theater air. Accordingly, an ad hoc committee of the American Society of Anesthesiologists (ASA) advised measures to reduce the trace concentrations of waste anesthetic gases in operating theaters (ASA advisory 1974).

But is this true? As I discussed in another page on this website, all these studies were retrospective studies based upon voluntary responses to questionaires. Not everyone responds to such questionaires, and those most likely to respond are those who have had problems. This rendered all these earlier studies suspect, and as discussed below, these study results have never been confirmed in properly conducted prospective studies. So what is the truth regarding exposure to:

Before discussing these questions, it is well worth looking at the statistics of pregnancies of women who are never exposed to anesthetic gases at all.

Chances of abnormal pregnancy outside the operating theater

Pregnancy is an important life event, so it is only natural for everyone to be concerned. A pregnant woman has many questions, hopes, and fears. All hope for the delivery of a happy healthy baby. But not all pregnancies end this way. So what are the normal incidences, or percentage chances of events such as miscarriage, of ectopic pregnancy, of stillbirth, or of giving birth to a child with a birth defect?

The table below gives the percentage chances for miscarriage, ectopic pregnancy, and stillbirth for all births in Denmark from 1978 to 1992 (Nybo Andersen-2000). These statistics are comparable to those of other developed Western countries.


Chance of miscarriage, ectopic pregnancy, and stillbirth from Danish data for the years 1978-1992 derived from Nybo Andersen-2000

Age groupChance of
Miscarriage (%)
Chance of
Ectopic Pregnancy (%)
Chance of
Stillbirth (%)
less than 2010.6%1.6%0.4%


This table clearly shows that the most ideal age range for a woman to have children is in her 20's. Increasing maternal age is strongly associated with increased chance of miscarriage or ectopic pregnancy. Factors other than age predisposing to miscarriage are:

This brings us to the subject of the chance of giving birth to an abnormal baby, otherwise termed a baby with a birth defect. The chances of giving birth to a baby with a birth defect in different parts of the world are given in the table below. As with the chances of miscarriage, the most optimal age range for any woman to have a baby is in her 20's.


Age group% Birth Defects
(Victoria 1983-1998)
% Birth Defects
(Singapore 1994-2000)
% Birth Defects
(Dallas-USA 1988-1994)
less than 203.5%2.8%3.5-3.7%


Trace concentrations of waste anesthetic gases and pregnancy - Current knowledge

Most women working in the stressful environment of operating theaters are younger women in their reproductive years. The tables above clearly show there is about a 10% chance of miscarriage and a 3% chance of giving birth to a child with a birth deficit. These figures are significant. They mean that in any operating theater complex where many women work, one or more of these women will certainly experience a miscarriage or give birth to a child with a birth defect, even if there is no pollution of the air with trace concentrations of anesthetic gases.

So what is the current state of knowledge regarding the effects of trace concentrations of anesthetic gases on pregnancy? Careful analyses of all studies reveals there is no relationship between the presence of trace concentrations of anesthetic gases and abnormal pregancies in women working in operating theaters. There is no increased chance of miscarriage, or of giving birth to babies with birth defects by women working in operating theaters, nor in the female partners of men working in operating theaters. Indeed, subsequent critical analyses of studies performed during the 1970's revealed many of them to be seriously flawed, rendering the conclusions of these studies very dubious indeed (Tannenbaum 1985, Mazze 1985, Buring 1985). And more recent studies fail to show any relationship between disturbances of pregnancy and trace concentrations of anesthetic gases at all (McGregor 2000). But what about pregnant women who undergo a surgical procedure under anesthesia?

Anesthesia and surgery during pregnancy

People never undergo anesthesia without subsequently undergoing a surgical procedure - people undergo anesthesia to make a surgical procedure possible. So the effects of anesthesia on a pregnant woman and her unborn child are actually the combined effects of anesthesia together with surgery.

Up to 2% of all pregnant women require surgery for all manner of conditions unrelated to their pregnancy, e.g. appendicits, broken bones, etc, etc, (Ne Mhuireachtaigh 2006). Surgeons perform these non-obstetrical operations upon pregnant women only for serious conditions threatening the life of the mother, or conditions causing serious disability if not performed at that moment. The normal policy is to wait until after delivery of the baby before performing any non-urgent surgery. So what are the statistics regarding anesthesia and surgery performed during pregnancy?

The conclusions drawn from these statistics are evident. Anesthesia and surgery during pregnancy is safe for the mother, and the chance of delivering a baby with a birth defect is unchanged by anesthesia and surgery. However, anesthesia and surgery performed during the first trimester of pregnancy is associated with a high rate of infant death, while anesthesia and surgery can induce premature labor when performed in later phases of pregnancy. So any decision to perform an operation during pregnancy, is determined by weighing the necessity for performing the operation against the higher than normal rate of fetal loss and prematurity.


Pregnancy & Anesthesia
Preoperative Problems
General problems
during anesthesia
Anesthesia & the Soul