Everyone needs to count what they are doing. This tells them what is going on, and lets them allocate resources wisely and detect warning trends. To do this effectively we need unambiguous definitions. This is not always easy. The UK, like all other countries, has its own legal definitions which sometimes differ from those in other countries and also alter from time to time. The World Health Organization (WHO) tries to coordinate international statistics by producing agreed definitions in its International Classification of Diseases (ICD) publications which are updated at approximately 10 yearly intervals. Here are a few of the more important definitions used in obstetric epidemiology. This chapter uses the same definitions as the UK Office of National Statistics (ONS) and consider some of the difficulties that they cause statisticians.
In the UK this is defined simply as 'a child born alive'. WHO says the same thing in more words - 'the complete expulsion or extraction from its mother of a product of conception, which after such separation, breathes or shows any other evidence of life, such as the beating of the heart, pulsation of the umbilical cord, or definite movement of voluntary muscles, whether or not the umbilical cord has been cut or the placenta is attached; each product of such a birth is considered live born. Twins both born alive count as two live births but a child who dies from asphyxia caused by shoulder dystocia after delivery of the head but before delivery of the body is not a live birth'.
There is no lower gestational age limit to the UK definition so a child of any gestational age which shows signs of life should be registered. This can occasionally lead to anomalies when for example a fetus of say 12 weeks is noticed to have a heart beat for some minutes after it has miscarried; although strictly a live birth, which should be registered as such and counted in the birth statistics, this offends against common sense.
The WHO does not interfere in national birth registrations but recommends that births only be included in national statistics if they weigh at least 500 g or have a ges-tational age of at least 22 weeks, so the problem does not arise. There were 639,721 live births registered in England and Wales in 2004.
The UK definition is wordy; 'a child which has issued forth from its mother after the 24th week of pregnancy and which did not at any time after being completely expelled from its mother breathe or show any other sign of life.' WHO uses the synonym 'fetal death' and defines this as 'death prior to the complete expulsion of extraction from its mother of a product of conception, irrespective of the duration of pregnancy; the death is indicated by the fact that after such separation the fetus does not breathe or show any other evidence of life, such as beating of the heart, pulsation of the umbilical cord, or definite movement of voluntary muscles'. Again such fetal deaths should only be included in national statistics if the weight was at least 500 g or the gestation at least 22 weeks.
The UK policy of including all fetuses delivered after a certain time point also leads to anomalies. A fetus that dies at 20 weeks but is delivered at 26 weeks should be registered as a stillbirth. But what about a twin pregnancy at 8 weeks in which one fetus dies at 12 weeks and at term a minute nodule of presumed fetus papyraceous is identified by microscopic examination of the placenta? Strictly this also should be registered as a stillbirth, but fortunately common sense usually prevails.
Once we have agreed what a live birth and a stillbirth are, birth is easy. It is defined as 'a live birth or a stillbirth'. Note that pregnancies are not recorded systematically in the UK, or most other countries, unless they end in live birth, stillbirth or legal abortion. Spontaneous miscarriages are rarely recorded at all, for the obvious reason that many happen at home some of which may not be recognized for what they are even by the mother.
WHO defines a maternal death as 'the death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the duration and the site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management, but not from accidental or incidental causes'. Since some deaths caused by pregnancy can occur much later than 42 days WHO defines late maternal death as those related to or aggravated by the pregnancy between 42 days and 1 year after delivery. For some purposes it may be useful to count all deaths among women who are pregnant or recently delivered, so there is also a category of pregnancy related deaths which includes all deaths from whatever cause during pregnancy or within 42 days of termination of pregnancy.
Finally maternal deaths are subdivided into direct deaths arising from the pregnancy itself or its complications or treatment, and indirect deaths from pre-existing disease or disease unrelated to the pregnancy.
We express maternal deaths as the ratio of deaths to 100,000 live births, rather than as a rate per 100,000 pregnancies. The latter might seem more logical since many maternal deaths occur in the absence of a live birth, but is not possible because pregnancies are not registered. The maternal mortality ratio in the UK, and most similar developed countries is around 10 per 100,000 live births, while in much of Africa and the developing world it lies between 500 and 1000 per 100,000. No other health statistic differs so much between developed and developing countries.
In the UK more detailed causes of deaths are collected in the long established triennial Confidential Enquiries into Maternal Deaths (CEMD) and the more recent Confidential Enquiries into Stillbirths and Deaths in Infancy (CESDI). The value of these sorts of studies is repeatedly shown. For example, it has recently been discovered that many previously unrecognized pregnancy-related deaths were probably suicides, making this the leading cause of maternal death in the UK .
The reliability of statistics on some other areas of medical activity is relatively poor and periodic national censuses are required. For example, national statistics on
Caesarean delivery are not routinely collected in the UK but the National Sentinel Caesarean Section Audit filled in many gaps.
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The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.