Use of Vital Statistics in Obstetrics

Updated: Dec 30, 2014
  • Author: Nevert Badreldin, MD, MS; Chief Editor: Christine Isaacs, MD  more...
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Overview

Overview

Many of the greatest advances in medicine have come as a result of public health research interventions. [1, 2] The ability to intervene in the health of populations is dependent upon development of appropriate tools for measuring health, illness, interventions, and outcomes. Only by standardizing communication can clinicians hope to target high-risk populations with effective interventions. Therefore, understanding the common language of public health is vital.

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Maternal Vital Statistics

Maternal vital statistics

Important measures of maternal health across a population include not only mortality and birth rates but also subtler measures, such as fertility rates and reproductive mortality rates, among others. [1] If used in a standardized fashion, this information allows comparison between groups with regard to the most vital function of any population—reproducing itself. Use of these measures also allows targeted interventions in order to improve outcomes. [3, 4, 5, 6] Except when specified below, the listed definitions are generated by the National Center for Health Statistics (NCHS) [7] with collaboration among international organizations such as the World Health Organization (WHO). [8]

Birth rate

Birth rate is defined as the number of births per 1,000 population. Of note, men are included in the population calculation. This is a gross measure of a population's growth. Less-developed areas tend to have higher birth rates. It is important, however, to interpret birth rates in the setting of infant and childhood mortality rates, which are disproportionally high in urban and poor populations worldwide. [8]

Fertility rate

The fertility rate is the number of live births per 1,000 women aged 15-44 years. This calculation is an attempt to measure the rate at which women of reproductive age are successfully reproducing. Births certainly occur in women outside this age range and can artificially curtail the numerator. However, including 10- or 51-year-old females would disproportionally expand the denominator. Of note, live births are specified. Although a woman with second-trimester miscarriages might be considered “fertile” by a reproductive endocrinologist, her deliveries would not be included in the fertility rate.

Maternal mortality ratio

The maternal mortality ratio is defined as the direct and indirect maternal deaths per 100,000 live births. The denominator for this statistic is 100,000 and not 1,000, as is the case with other vital statistics — this is a triumph of modern medicine. A condition in which both mother and fetus are lost would both increase the numerator (maternal death) and decrease the denominator (live birth). Because the rate is very low in developed nations (approximately 28 deaths per 100,000 population in the United States in 2013 [8] ), a different methodology would have little effect on the data. However, 99% of all maternal deaths occur in developing countries, and thus some authors have argued for a denominator that includes liveborn and stillborn infants. [7, 8]

Direct maternal death rate

Direct maternal death rates are calculated as the number of direct maternal deaths per 100,000 live births. This statistic is defined as death from complications of pregnancy, delivery, or the puerperium period. Implicit is the notion that had the woman not been pregnant, the death would not have occurred. In developed countries, direct maternal deaths are most commonly caused by hemorrhage, hypertensive disorders, and embolic events. In contrast, in developing countries, sepsis replaces embolic events as a leading cause of maternal deaths. [9]

Indirect maternal death rate

The indirect maternal death rate is defined as the number of indirect maternal deaths per 100,000 live births. Indirect deaths often represent underlying medical conditions aggravated, but not caused by, the pregnancy, including complications from connective-tissue disease or cardiac conditions, in which the underlying pathology is independent of the pregnancy, but it was likely to have been exacerbated by pathophysiologic changes of pregnancy.

It has been estimated that half of direct maternal deaths in the United States may be preventable through early diagnosis and appropriate medical care of pregnancy complications. [10] In contrast, indirect maternal deaths may simply reflect the magnitude of the underlying disorder and may paradoxically reflect advances in medical care that have allowed women with comorbidities to achieve reproductive age and to undertake pregnancy.

Nonmaternal death rate

Nonmaternal death rates are calculated as the number of nonmaternal deaths per 100,000 live births. This rate measures only deaths of pregnant or postpartum women that were neither caused, nor aggravated by, the pregnancy. Examples of this would be deaths secondary to motor vehicle accidents or homicides.

By distinguishing nonmaternal, direct, and indirect maternal death rates, a much more sensitive picture of a population's health needs emerges than would be possible with a lumped rate.

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Infant Statistics

Infant statistics

The definitions listed below are not intended to carry any moral, religious, or philosophical significance but rather to help clinicians to speak a common language.

Abortion

This category is not defined by the National Center for Health Statistics; rather it is defined by each state as part of its requirements for completion of birth and death certificates. The most common definition of an abortion is any loss of a fetus that is younger than 20 weeks' completed gestational age. Because many states allow elective termination of pregnancy beyond 20 weeks' estimated gestational age, an "or" provision may exist which would allow inclusion of elective termination beyond 20 weeks' gestation as an abortion. In states without this language in their certification process, this delivery would be coded as a stillbirth or live birth even though it was deliberately initiated.

Conversely, some states include any sign of life, regardless of gestational age, to represent a live birth. This would include the 18-week fetus that takes one reflex gasp after delivery. Because these deliveries carry a 0% survival rate under any circumstances, this definition can artificially inflate a region's infant and neonatal mortality rates.

Induced termination of pregnancy

Induced termination of pregnancy is defined as the purposeful interruption of an intrauterine pregnancy with the intention other than to produce a live-born infant and which does not result in a live birth. [11] Unsafe abortion is a major cause of maternal death and accounts for one in eight maternal deaths yearly. Almost all of these deaths occur in developing areas. Maternal death is rare where abortion is legal and access is nonrestrictive, as well as when pregnancy terminations are carried out by skilled health professionals. [12]

Preterm infant

A preterm infant is defined as an infant delivered between 20 weeks' and 36 weeks 6 days' gestational age. This group can be further subdivided into early preterm and late preterm infants.

Early preterm is defined as a gestational age between 20 weeks and 33 weeks 6 days at the time of delivery, whereas late preterm is defined as a gestational age between 34 weeks and 36 weeks 6 days. The risk of poor birth outcomes decreases with advancing gestational age, and it is substantially greater for early preterm infants. [13]

Postterm infant

The definition of a postterm pregnancy is one that progresses beyond 42 weeks' completed gestational age. Postterm infants have a higher rate of perinatal morbidity and mortality. [14]

Stillbirth

A stillbirth is defined as a delivery at or greater than 20 weeks' gestation if the gestational age is known, or a weight greater than or equal to 350 grams if the gestational age is not known, in which the infant displays no sign of life as indicated by the absence of breathing, heart beats, pulsation of the umbilical cord, or definite movements of voluntary muscles. The cutoff of 350 grams is the 50th percentile for weight at 20 weeks of gestation. However, note that there is no complete uniformity among states with regard to birth weight and gestational age criteria for reporting fetal deaths. [7, 15]

Live birth

Delivery after 20 weeks' gestational age in which any fetal activity is noted is classified as a live birth. The lower limit of reasonable viability currently remains around 23 weeks' gestational age. Thus, a spontaneous delivery before that time with reflex motion but no ability to survive with or without intervention would nonetheless be considered a live birth.

Fetal death rate (stillbirth rate)

The fetal death rate (stillbirth rate) statistic measures the number of stillbirths per 1,000 infants born.

Neonatal mortality rate

The neonatal mortality rate measures infant deaths between 0-28 days of life per 1,000 live births. The neonatal mortality rate reflects losses between the moment of live birth and 28 days of life. This rate is often divided into early (first 7 d) and late (8-28 d) rates, as etiologies within these two categories vary. This is slightly different number than the fetal death rate, which is measured per 1,000 total births.

Perinatal mortality rate

The perinatal mortality rate is calculated as the number of fetal deaths plus neonatal deaths per 1,000 total births. This statistic attempts to correct the intrinsic problem of heroic attempts at rescue. The neonatal mortality rate might be quite high, for example, if pediatricians at an institution attempt to resuscitate all 22-week infants regardless of signs of life at delivery.

Infant mortality rate

Infant mortality rates are calculated as the number of infants who die prior to their first birthday per 1,000 live births. In developing countries, the losses due to infectious diseases far outweigh the inability of technology to deal with preterm births or congenital anomalies. Thus, infant mortality is often one of the sentinel indicators used to evaluate a population's overall health and access to health care. [16, 17]

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Conclusion

Understanding how a population is coping with the burdens of reproduction is vital. High-quality population based data are essential in the interpretation of obstetric and maternal care. This valuable insight can provide populations with the opportunity to intervene for improved outcomes for women and infants and, therefore, communities as a whole. [3]

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