Early Pregnancy Loss: Incidence

Introduction

For both the physician and the patient, early pregnancy loss is a frustrating and heart-wrenching experience. Early pregnancy loss is unfortunately the most common complication of human gestation, occurring in at least 75% of all women trying to conceive. Most of these losses are unrecognized and occur before or with the next expected menses. Of those that are recognized, 15-20% are spontaneous abortions (SABs) or ectopic pregnancies diagnosed after the pregnancy is clinically recognized. Approximately 5% of couples trying to conceive have 2 consecutive miscarriages, and approximately 1% of couples have 3 or more consecutive losses.

Early pregnancy loss is defined as the termination of pregnancy before 20 weeks' gestation or with a fetal weight of <500>

Table 1: Terms Used to Describe Pregnancy Loss

Table

Term	Definition
Chemical pregnancy loss	Loss of a biochemically evident pregnancy
Early pregnancy loss	Abortion of the first trimester, loss of a histologically recognized pregnancy, or a loss based on ultrasonographic findings
SAB	Pregnancy loss before 20 weeks' gestation, as based on last menstrual period
Habitual or recurrent abortion	3 or more consecutive SABs
Stillbirth	Pregnancy loss after 20 weeks' gestation (Neonatal loss is the death of a liveborn fetus.)

Term	Definition
Chemical pregnancy loss	Loss of a biochemically evident pregnancy
Early pregnancy loss	Abortion of the first trimester, loss of a histologically recognized pregnancy, or a loss based on ultrasonographic findings
SAB	Pregnancy loss before 20 weeks' gestation, as based on last menstrual period
Habitual or recurrent abortion	3 or more consecutive SABs
Stillbirth	Pregnancy loss after 20 weeks' gestation (Neonatal loss is the death of a liveborn fetus.)

Incidence

The incidence of spontaneous miscarriage is10-15%, whereas the rate of recurrent miscarriage is 3-5%.

Most studies demonstrate a spontaneous miscarriage rate of 10-15%. However, the true rate of early pregnancy loss is close to 50% because of the high number of chemical pregnancies that are not recognized in the 2-4 weeks after conception. Most of these pregnancy failures are due to gamete failure (eg, sperm or oocyte dysfunction). In a classic study by Wilcox et al in 1988, 221 women were followed up during 707 total menstrual cycles. A total of 198 pregnancies were achieved. Of these, 43 (22%) were lost before the onset of menses, and another 20 (10%) were clinically recognized losses.

The likelihood for an SAB increases with each successive abortion. Data from various studies indicate that, after 1 SAB, the baseline risk of a couple having another SAB is approximately 15%. However, if 2 SABs occur, the subsequent risk increases to approximately 30%. The rate is higher for women who have not had at least 1 liveborn infant. Several groups have estimated that the risk of pregnancy loss after 3 successive abortions is 30-45%. Therefore, controversy exists regarding how many pregnancy losses should occur before a diagnostic evaluation is considered. One could argue that the diagnostic evaluation should be performed after 2 losses rather than 3 because diagnostic yields after 2 versus 3 miscarriages are identical.