Parity derived for pregnant women using historical administrative hospital data: accuracy varied among patient groups

Use of induction of labour and emergency caesarean section and perinatal outcomes in English maternity services: a national hospital-level study

OBJECTIVES

To assess the association between hospital-level rates of induction of labour and emergency caesarean section, as measures of "practice style", and rates of adverse perinatal outcomes.

DESIGN

National study using electronic maternity records.

SETTING

English National Health Service.

PARTICIPANTS

Hospitals providing maternity care to women between April 2015 and March 2017.

MAIN OUTCOME MEASURES

Stillbirth, admission to a neonatal unit, and babies receiving mechanical ventilation.

RESULTS

Among singleton term births, the risk of stillbirth was 0.15%; of admission to a neonatal unit 5.4%; and of mechanical ventilation 0.54%. There was considerable between-hospital variation in the induction of labour rate (minimum 17.5%, maximum 40.7%) and the emergency caesarean section rate (minimum 5.6%, maximum 17.1%). Women who gave birth in hospitals with a higher induction of labour rate had better perinatal outcomes. For each 5%-point increase in induction, there was a decrease in the risk of term stillbirth by 9% (OR 0.91; 95% CI 0.85 to 0.97) and mechanical ventilation by 14% (OR 0.86; 95% CI 0.79 to 0.94). There was no significant association between hospital-level induction of labour rates and neonatal unit admission at term (p>0.05). There was no significant association between hospital-level emergency caesarean section rates and adverse perinatal outcomes (p always >0.05).

CONCLUSIONS

There is considerable between-hospital variation in the use of induction of labour and emergency caesarean section. Hospitals with a higher induction rate had a lower risk of adverse birth outcomes. A similar association was not found for caesarean section.

Maternal and perinatal outcomes of pregnant women with SARS-CoV-2 infection at the time of birth in England: national cohort study

BACKGROUND

Some studies have suggested that women with SARS-CoV-2 infection during pregnancy are at increased risk of adverse pregnancy and neonatal outcomes, but these associations are still not clear.

OBJECTIVE

This study aimed to determine the association between SARS-CoV-2 infection at the time of birth and maternal and perinatal outcomes.

STUDY DESIGN

This is a population-based cohort study in England. The inclusion criteria were women with a recorded singleton birth between May 29, 2020, and January 31, 2021, in a national database of hospital admissions. Maternal and perinatal outcomes were compared between pregnant women with a laboratory-confirmed SARS-CoV-2 infection recorded in the birth episode and those without. Study outcomes were fetal death at or beyond 24 weeks' gestation (stillbirth), preterm birth (<37 weeks' gestation), small for gestational age infant (small for gestational age; birthweight at the <tenth centile), preeclampsia or eclampsia, induction of labor, mode of birth, specialist neonatal care, composite neonatal adverse outcome indicator, maternal and neonatal length of hospital stay after birth (3 days or more), and 28-day neonatal and 42-day maternal hospital readmission. Adjusted odds ratios and their 95% confidence interval for the association between SARS-CoV-2 infection status and outcomes were calculated using logistic regression, adjusting for maternal age, ethnicity, parity, preexisting diabetes mellitus, preexisting hypertension, and socioeconomic deprivation measured using the Index of Multiple Deprivation 2019. Models were fitted with robust standard errors to account for hospital-level clustering. The analysis of the neonatal outcomes was repeated for those born at term (≥37 weeks' gestation) because preterm birth has been reported to be more common in pregnant women with SARS-CoV-2 infection.

RESULTS

The analysis included 342,080 women, of whom 3527 had laboratory-confirmed SARS-CoV-2 infection. Laboratory-confirmed SARS-CoV-2 infection was more common in women who were younger, of non-White ethnicity, primiparous, or residing in the most deprived areas or had comorbidities. Fetal death (adjusted odds ratio, 2.21; 95% confidence interval, 1.58-3.11; P<.001) and preterm birth (adjusted odds ratio, 2.17; 95% confidence interval, 1.96-2.42; P<.001) occurred more frequently in women with SARS-CoV-2 infection than those without. The risk of preeclampsia or eclampsia (adjusted odds ratio, 1.55; 95% confidence interval, 1.29-1.85; P<.001), birth by emergency cesarean delivery (adjusted odds ratio, 1.63; 95% confidence interval, 1.51-1.76; P<.001), and prolonged admission after birth (adjusted odds ratio, 1.57; 95% confidence interval, 1.44-1.72; P<.001) were significantly higher for women with SARS-CoV-2 infection than those without. There were no significant differences (P>.05) in the rate of other maternal outcomes. The risk of neonatal adverse outcome (adjusted odds ratio, 1.45; 95% confidence interval, 1.27-1.66; P<.001), need for specialist neonatal care (adjusted odds ratio, 1.24; 95% confidence interval, 1.02-1.51; P=.03), and prolonged neonatal admission after birth (adjusted odds ratio, 1.61; 95% confidence interval, 1.49-1.75; P<.001) were all significantly higher for infants with mothers with laboratory-confirmed SARS-CoV-2 infection. When the analysis was restricted to pregnancies delivered at term (≥37 weeks), there were no significant differences in neonatal adverse outcome (P=.78), need for specialist neonatal care after birth (P=.22), or neonatal readmission within 4 weeks of birth (P=.05). Neonates born at term to mothers with laboratory-confirmed SARS-CoV-2 infection were more likely to have prolonged admission after birth (21.1% compared with 14.6%; adjusted odds ratio, 1.61; 95% confidence interval, 1.49-1.75; P<.001).

CONCLUSION

SARS-CoV-2 infection at the time of birth is associated with higher rates of fetal death, preterm birth, preeclampsia, and emergency cesarean delivery. There were no additional adverse neonatal outcomes, other than those related to preterm delivery. Pregnant women should be counseled regarding risks of SARS-CoV-2 infection and should be considered a priority for vaccination.

Developing a national birth cohort for child health research using a hospital admissions database in England: The impact of changes to data collection practices

BACKGROUND

National birth cohorts derived from administrative health databases constitute unique resources for child health research due to whole country coverage, ongoing follow-up and linkage to other data sources. In England, a national birth cohort can be developed using Hospital Episode Statistics (HES), an administrative database covering details of all publicly funded hospital activity, including 97% of births, with longitudinal follow-up via linkage to hospital and mortality records. We present methods for developing a national birth cohort using HES and assess the impact of changes to data collection over time on coverage and completeness of linked follow-up records for children.

METHODS

We developed a national cohort of singleton live births in 1998-2015, with information on key risk factors at birth (birth weight, gestational age, maternal age, ethnicity, area-level deprivation). We identified three changes to data collection, which could affect linkage of births to follow-up records: (1) the introduction of the "NHS Numbers for Babies (NN4B)", an on-line system which enabled maternity staff to request a unique healthcare patient identifier (NHS number) immediately at birth rather than at civil registration, in Q4 2002; (2) the introduction of additional data quality checks at civil registration in Q3 2009; and (3) correcting a postcode extraction error for births by the data provider in Q2 2013. We evaluated the impact of these changes on trends in two outcomes in infancy: hospital readmissions after birth (using interrupted time series analyses) and mortality rates (compared to published national statistics).

RESULTS

The cohort covered 10,653,998 babies, accounting for 96% of singleton live births in England in 1998-2015. Overall, 2,077,929 infants (19.5%) had at least one hospital readmission after birth. Readmission rates declined by 0.2% percentage points per annual quarter in Q1 1998 to Q3 2002, shifted up by 6.1% percentage points (compared to the expected value based on the trend before Q4 2002) to 17.7% in Q4 2002 when NN4B was introduced, and increased by 0.1% percentage points per annual quarter thereafter. Infant mortality rates were under-reported by 16% for births in 1998-2002 and similar to published national mortality statistics for births in 2003-2015. The trends in infant readmission were not affected by changes to data collection practices in Q3 2009 and Q2 2013, but the proportion of unlinked mortality records in HES and in ONS further declined after 2009.

DISCUSSION

HES can be used to develop a national birth cohort for child health research with follow-up via linkage to hospital and mortality records for children born from 2003 onwards. Re-linking births before 2003 to their follow-up records would maximise potential benefits of this rich resource, enabling studies of outcomes in adolescents with over 20 years of follow-up.

Risk of complicated birth at term in nulliparous and multiparous women using routinely collected maternity data in England: cohort study

OBJECTIVES

To determine the rate of complicated birth at term in women classified at low risk according to the National Institute for Health and Care Excellence guideline for intrapartum care (no pre-existing medical conditions, important obstetric history, or complications during pregnancy) and to assess if the risk classification can be improved by considering parity and the number of risk factors.

DESIGN

Cohort study using linked electronic maternity records.

PARTICIPANTS

276 766 women with a singleton birth at term after a trial of labour in 87 NHS hospital trusts in England between April 2015 and March 2016.

MAIN OUTCOME MEASURE

A composite outcome of complicated birth, defined as a birth with use of an instrument, caesarean delivery, anal sphincter injury, postpartum haemorrhage, or Apgar score of 7 or less at five minutes.

RESULTS

Multiparous women without a history of caesarean section had the lowest rates of complicated birth, varying from 8.8% (4879 of 55 426 women, 95% confidence interval 8.6% to 9.0%) in those without specific risk factors to 21.8% (613 of 2811 women, 20.2% to 23.4%) in those with three or more. The rate of complicated birth was higher in nulliparous women, with corresponding rates varying from 43.4% (25  805 of 59 413 women, 43.0% to 43.8%) to 64.3% (364 of 566 women, 60.3% to 68.3%); and highest in multiparous women with previous caesarean section, with corresponding rates varying from 42.9% (3426 of 7993 women, 41.8% to 44.0%) to 66.3% (554 of 836 women, 63.0% to 69.5%).

CONCLUSIONS

Nulliparous women without risk factors have substantially higher rates of complicated birth than multiparous women without a previous caesarean section even if the latter have multiple risk factors. Grouping women first according to parity and previous mode of birth, and then within these groups according to presence of specific risk factors would provide greater and more informed choice to women, better targeting of interventions, and fewer transfers during labour than according to the presence of risk factors alone.

A step-wise approach to developing indicators to compare the performance of maternity units using hospital administrative data

Hospital administrative data are attractive for comparing performance of maternity units because of their often large sample sizes, lack of selection bias and the relatively low costs of accessing these data compared with conducting primary data collection. However, using administrative data to develop indicators can also present challenges including varying data quality, the limited detail on clinical risk factors and a lack of structural and user experience measures. This review illustrates how to develop performance indicators for maternity units using hospital administrative data, including methods to address the challenges that administrative data pose.

TWEETABLE ABSTRACT

How to develop maternity indicators from administrative data.

Hospital admission for hyperemesis gravidarum: a nationwide study of occurrence, reoccurrence and risk factors among 8.2 million pregnancies

STUDY QUESTION

What are the maternal risk factors for hyperemesis gravidarum (HG) hospital admission, readmission and reoccurrence in a following pregnancy?

SUMMARY ANSWER

Young age, less socioeconomic deprivation, nulliparity, Asian or Black ethnicity, female fetus, multiple pregnancy, history of HG in a previous pregnancy, thyroid and parathyroid dysfunction, hypercholesterolemia and Type 1 diabetes are all risk factors for HG.

WHAT IS KNOWN ALREADY

Women with Black or Asian ethnicity, of young age, carrying multiple babies or singleton females, with Type 1 diabetes or with a history of HG were previously reported to be at higher risk of developing HG; however, most evidence is from small studies. Little is known about associations with other comorbidities and there is controversy over other risk factors such as parity. Estimates of HG prevalence vary and there is a little understanding of the risks of HG readmission in a current pregnancy and reoccurrence rates in subsequent pregnancies, all of which are needed for planning measures to reduce onset or worsening of the condition.

STUDY DESIGN, SIZE, DURATION

We performed a population-based cohort study of pregnancies ending in live births and stillbirths using prospectively recorded secondary care records (Hospital Episode Statistics) from England. We analysed those computerized and anonymized clinical records from over 5.3 million women who had one or more pregnancies between 1997 and 2012.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We obtained 8 215 538 pregnancies from 5 329 101 women of reproductive age, with a total of 186 800 HG admissions occurring during 121 885 pregnancies. Multivariate logistic regression with generalized estimating equations was employed to estimate odds ratios (aOR) to assess sociodemographic, pregnancy and comorbidity risk factors for HG onset, HG readmission within a pregnancy and reoccurrence in a subsequent pregnancy.

MAIN RESULTS AND THE ROLE OF CHANCE

Being younger, from a less socioeconomically deprived status, of Asian or Black ethnicity, carrying a female fetus or having a multiple pregnancy all significantly increased HG and readmission risk but only ethnicity increased reoccurrence. Comorbidities most strongly associated with HG were parathyroid dysfunction (aOR = 3.83, 95% confidence interval 2.28-6.44), hypercholesterolemia (aOR = 2.54, 1.88-3.44), Type 1 diabetes (aOR = 1.95, 1.82-2.09), and thyroid dysfunction (aOR = 1.85, 1.74-1.96). History of HG was the strongest independent risk factor (aOR = 4.74, 4.46-5.05). Women with higher parity had a lower risk of HG compared with nulliparous women (aOR = 0.90, 0.89-0.91), which was not explained by women with HG curtailing further pregnancies.

LIMITATIONS, REASONS FOR CAUTION

Although this represents the largest population-based study worldwide on the topic, the results could have been biased by residual and unmeasured confounding considering that some potential important risk factors such as smoking, BMI or prenatal care could not be measured with these data. Underestimation of non-routinely screened comorbidities such as hypercholesterolemia or thyroid dysfunction could also be a cause of selection bias.

WIDER IMPLICATIONS OF THE FINDINGS

The estimated prevalence of 1.5% from our study was similar to the average prevalence reported in the literature and the representativeness of our data has been validated by comparison to national statistics. Also the prevalence of comorbidities was mostly similar to other studies estimating these in the UK and other developed countries. Women with Black or Asian ethnicity, of young age, carrying multiple babies or singleton females, with Type 1 diabetes or with history of HG were confirmed to be at higher risk of HG with an unprecedented higher statistical power. We showed for the first time that socioeconomic status interacts with maternal age, that hypercholesterolemia is a potential risk factor for HG and that carrying multiple females increases risk of hyperemesis compared with multiple males. We also provided robust evidence for the association of parity with HG. Earlier recognition and management of symptoms via gynaecology day-case units or general practitioner services can inform prevention and control of consequent hospital admissions.

STUDY FUNDING/COMPETING INTERESTS

The work was founded by The Rosetrees Trust and the Stoneygate Trust. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. C.N.-P. reports personal fees from Sanofi Aventis, Warner Chilcott, Leo Pharma, UCB and Falk, outside the submitted work and she is one of the co-developers of the RCOG Green Top Guideline on HG; all other authors did not report any potential conflicts of interest.

TRIAL REGISTRATION NUMBER

Not applicable.