eMedicine Specialties > Obstetrics and Gynecology > General Obstetrics

Use of Vital Statistics in Obstetrics

Deborah Lyon, MD, Director, Division of Benign Gynecology, Associate Professor, Department of Obstetrics and Gynecology, University of Florida Health Science Center at Jacksonville

Updated: Dec 3, 2007

Introduction

Many of the greatest advances in medicine have come as a result of public health interventions rather than individual treatments. The ability to intervene in the health of populations is dependent upon development of appropriate tools for measuring health, illness, and interventions. Only by standardizing communication on such issues as infant mortality can physicians hope to target high-risk populations with effective interventions. Despite the lack of clinical glamour associated with the subject of vital statistics, understanding the common language of public health is vital.

Maternal Vital Statistics

Important measures of maternal health across a population include not only the obvious mortality and birth rates but also subtler measures, including fertility rate and reproductive mortality rate. If used in a standardized fashion, this information allows comparison between 2 groups with regard to the most vital function of any population—reproducing itself. Use of these measures also allows targeted interventions to improve outcomes in a way that might be missed if medicine were practiced only one patient at a time. Except when specified below, the listed definitions are generated by the National Center for Health Statistics with collaboration among international organizations such as the World Health Organization.

Birth rate

The birth rate is calculated as number of births per 1000 population. It includes men in the population and is a gross measure of a population's growth rate. Less-developed areas tend to have very high birth rates, but these rates cannot be interpreted without knowing the infant and childhood mortality rates as well.

Fertility rate

The fertility rate is the number of live births per 1000 women aged 15-44 years and is an attempt to measure the rate at which women of reproductive age are successfully reproducing. Although births certainly occur in women outside this age range (thus, the numerator in the equation is artificially curtailed), including 10- or 51-year-old females would unfairly expand the denominator. Of note, live births are specified. While a woman with 3 second-trimester miscarriages would be considered fertile by a reproductive endocrinologist, her deliveries would not be included in the fertility rate.

Maternal mortality rate

The maternal mortality statistic measures the number of deaths that are directly or indirectly related to pregnancy. The denominator for this statistic is 100,000 live births and not 1000, as is the case with most other vital statistics; this is a triumph of modern medicine. This statistic is limited by its denominator because 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 so low in developed nations (approximately 9 deaths per 100,000 population in the United States), a different methodology would have little effect on the data. In less-developed areas, some authors have argued for a denominator that includes liveborn and stillborn infants.

Direct maternal death rate

This statistic is defined as death from complications of pregnancy, delivery, or the puerperium. Implicit is the notion that had the woman not been pregnant, the death would not have occurred. Complications such as preeclampsia, hemorrhage, and chorioamnionitis would be considered direct causes of maternal death, as would any complications arising from their treatment. The denominator is per 100,000 live births.

Indirect maternal death rate

Differentiating these deaths from direct maternal mortality is important, as indirect deaths often represent underlying medical conditions aggravated but not caused by the pregnancy. This would include complications from connective-tissue disease or cardiac conditions, in which the underlying pathology is independent of the pregnancy but was likely to have been aggravated by it. Virtually all direct maternal deaths demand intense scrutiny because most can be shown to have been preventable under optimal circumstances. Indirect maternal deaths, however, may simply reflect the magnitude of the underlying disorder and may paradoxically reflect the remarkable advances in medical care that allow these women to achieve reproductive age and, in some cases, to voluntarily undertake pregnancy in the face of enormous disadvantages. The denominator is per 100,000 live births.

Nonmaternal death rate

From the obstetrical perspective, this statistic is essential, but it would appear most odd if observed in a list by someone not attuned to the perspective of obstetrical public health. One would assume that nonmaternal deaths include all deaths in nonmothers. In fact, this rate measures only deaths of pregnant or postpartum women and is designed to capture those deaths that were neither caused by nor aggravated by the pregnancy (eg, motor vehicle accidents, homicides). By distinguishing 3 maternal death rates, a much more sensitive picture of a population's health needs emerges than would be possible with a lumped rate. As in the above cases, the denominator is per 100,000 live births.

Reproductive mortality rate

Sadly, many deaths occur from attempts to avoid pregnancy as well as from pregnancy itself. In fact, in the field of obstetrics, most contraceptive risks are evaluated for risk in comparison to pregnancy rather than in comparison to no intervention. Unfortunately, many internists and family practitioners forget this when counseling women about medication risks. To capture the risks of being a woman of reproductive age, the reproductive mortality rate measures deaths resulting from contraceptive use plus direct maternal deaths per 100,000 women. This is perhaps the most sensitive measure of a population's ability to provide safety for its most vulnerable and valuable segment.

Infant Statistics

Infant mortality is probably the most commonly quoted vital statistic in lay conversation. While important information is certainly presented in this statistic, care must be taken to distinguish it from, and to take into consideration, other measures of a population's ability to nourish its next generation. If orderly and reproducible methodology is to be employed, a certain arbitrariness to definitions must exist, which is not a problem with a statistic such as maternal mortality. The definitions listed below are not intended to carry any moral, religious, or philosophical significance but rather to help us speak a common language. Abortion This category is not defined by the National Center for Health Statistics but 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 less than 20 weeks' completed gestational age (since last menstrual period) or that weighs less than 500 grams.

Because many states allow elective termination of pregnancy beyond 20 weeks' estimated gestational age (EGA), an "or" provision may exist, which would allow inclusion of, for instance, a 24-week elective termination as an abortion. In states without this language in their certification process, this delivery would be coded as a stillbirth or livebirth 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. Since these deliveries carry a 0% survival rate under any circumstances, this definition artificially inflates a region's infant and neonatal mortality rates.

By convention in departments of obstetrics and gynecology, abortions are classified as gynecologic procedures. An induction at 19 weeks' EGA for lethal anomalies, even though carried out in the labor and delivery department using obstetrical language and tools, is classified as a gynecologic procedure.

Preterm infant

Preterm infant is another arbitrary definition because a subtle gradient of maturity exists. Most states define premature as a delivery before 37 completed weeks' gestational age, although the vast majority of babies born after 35 weeks' EGA have uncomplicated perinatal courses.

Postterm infant

The generally accepted definition of a postterm pregnancy is one that progresses beyond 42 weeks' completed gestational age based on last menstrual period (LMP). In practice, many clinicians use a lower cutoff such as 41 weeks' EGA when LMP is certain.

Stillbirth

Delivery after 20 weeks' EGA (and in some states, more than 500 g birthweight) in which the infant displays no sign of life (gasping, muscular activity, cardiac activity) is considered a stillbirth.

Live birth

Delivery after 20 weeks' EGA in which any activity is noted is classified as a live birth, with the possible caveats noted under Abortion. This is a difficult definition, as the lower limit of reasonable viability currently remains around 23 weeks' EGA. Thus, a spontaneous delivery at 21 weeks' EGA 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 number of stillbirths per 1000 infants (live and still) born.

Neonatal mortality rate

The neonatal mortality rate reflects losses between the moment of birth and 28 days of life (inclusive). The denominator is 1000 live births, a slightly different number than the fetal death rate (which is per 1000 births). This rate is often divided into early (first 7 d) and late (8-28 d) rates, as etiologies within these 2 categories vary somewhat.

Perinatal mortality rate

This statistic attempts to correct the intrinsic problem of heroic attempts at rescue. The neonatal mortality rate might be quite high, for example, if the pediatricians at an institution attempt to resuscitate all 22-week infants regardless of signs of life at delivery. Perinatal mortality adds fetal deaths and neonatal deaths per 1000 total births.

Infant mortality rate

This is a more global measure than those described above. It designates infants who die prior to their first birthday. The denominator is 1000 live births. In developing countries, the losses due to infectious disease far outweigh the inability of technology to deal with preterm birth 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.

Conclusion

When viewed as a list of definitions, vital statistics appear unspeakably dry; however, their name tells their story. Understanding how we are coping as a population with the burdens of reproduction is vital. Without this insight, many valuable opportunities to intervene may be missed, opportunities which ultimately may benefit individuals.

On a trip to Egypt in the 1980s, I was told by my tour guide that the infant mortality rate was 95 deaths per thousand. As sad as that number sounds, I was probably the only person on the bus who had the information to really drive home its significance; the infant mortality rate in the United States was about 11 deaths per thousand at that time. As remote as numbers seem from the business of clinical medicine, surely no physician's heart could fail to be stirred by that contrast, and surely more action has been sparked by making those numbers available to the world than would occur if we all "just take good care of our patients." Part of the appropriate business of medicine is to keep good records and to understand our own measures.

References

Pritchard JA, MacDonald PC, Gant NF. Obstetrics in broad perspective. In: Williams Obstetrics. 22^nd ed. New York, NY: McGraw-Hill; 2005.
National Center for Health Statistics -- monitoring the nation's health. National Center for Health Statistics. Available at http://www.cdc.gov/nchs/. Accessed September 28, 2007.
Health statistics and health information systems. World Health Organization Mortality Tables. Available at http://www.who.int/healthinfo/morttables/en/index.html. Accessed September 28, 2007.
Schoendorf KC, Branum AM. The use of United States vital statistics in perinatal and obstetric research. Am J Obstet Gynecol. Apr 2006;194(4):911-5. [Medline].
Cahill AG, Macones GA. Vital considerations for the use of vital statistics in obstetrical research. Am J Obstet Gynecol. Apr 2006;194(4):909-10. [Medline].

Keywords

mortality rates, birth rates, fertility rates, reproductive mortality rates, targeted interventions, obstetrical public health, maternal mortality rate, indirect maternal death rate, nonmaternal death rate, abortion, preterm infant, postterm infant, stillbirth, live birth, fetal death rate, stillbirth rate, neonatal mortality rate, perinatal mortality rate, infant mortality rate

Contributor Information and Disclosures

Author

Deborah Lyon, MD, Director, Division of Benign Gynecology, Associate Professor, Department of Obstetrics and Gynecology, University of Florida Health Science Center at Jacksonville
Deborah Lyon, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, Association of American Medical Colleges, Association of Professors of Gynecology and Obstetrics, and Florida Medical Association
Disclosure: Nothing to disclose.

Medical Editor

Robert K Zurawin, MD, Associate Professor, Director of Fellowship Programs, Minimally Invasive Surgery, Department of Obstetrics and Gynecology, Baylor College of Medicine; Chief of Gynecology, Texas Children's Hospital
Robert K Zurawin, MD is a member of the following medical societies: American Association of Gynecologic Laparoscopists, American College of Obstetricians and Gynecologists, American Society for Reproductive Medicine, Association of Professors of Gynecology and Obstetrics, Central Association of Obstetricians and Gynecologists, Harris County Medical Society, North American Society for Pediatric and Adolescent Gynecology, and Texas Medical Association
Disclosure: Johnson and Johnson Honoraria Speaking and teaching; Conceptus Honoraria Speaking and teaching

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

A David Barnes, MD, PhD, MPH, FACOG, Consulting Staff, Department of Obstetrics and Gynecology, Mammoth Hospital, Mammoth Lakes, California, Pioneer Valley Hospital, Salt Lake City, Utah, Warren General Hospital, Warren, Pennsylvania and Mountain West Hospital, Tooele, Utah
A David Barnes, MD, PhD, MPH, FACOG is a member of the following medical societies: American College of Forensic Examiners, American College of Obstetricians and Gynecologists, American Medical Association, Association of Military Surgeons of the US, and Utah Medical Association
Disclosure: Nothing to disclose.

CME Editor

Frederick B Gaupp, MD, Consulting Staff, Department of Family Practice, Assumption Community Hospital
Frederick B Gaupp, MD is a member of the following medical societies: American Academy of Family Physicians
Disclosure: Nothing to disclose.

Chief Editor

David Chelmow, MD, Professor of Obstetrics and Gynecology, Tufts University School of Medicine; Program Director, Tufts University Affiliated Hospitals OB/GYN Residency Program; Chair, Tufts University Health Sciences Campus Institutional Review Board
David Chelmow, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Medical Association, Association of Professors of Gynecology and Obstetrics, Massachusetts Medical Society, Phi Beta Kappa, Sigma Xi, Society for Gynecologic Investigation, and Society for Medical Decision Making
Disclosure: Nothing to disclose.

Further Reading