Influence of parity on the obstetric performance of mothers aged 40 years and above

B.C.P. Chan1,3 and T.T. Lao2

1 Department of Obstetrics & Gynaecology, Tsan Yuk Hospital, and 2 Department of Obstetrics & Gynaecology, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
We reviewed the delivery records of 205 mothers aged 40 years and above who delivered from 1st January 1994 to 31st December 1996 to examine the influence of parity on their obstetric performance. There were 51 (24.9%) primiparous mothers. The incidences of antenatal complications (antepartum haemorrhage, hypertensive disorder, glucose intolerance, prematurity), labour performance (type of labour, mode of delivery) and neonatal outcome (birth weight, Apgar scores, neonatal intensive care unit admission, perinatal mortality) were compared between the 51 (24.9%) primiparous and the 154 (75.1%) multiparous mothers. Higher incidences of antepartum haemorrhage (17.6 versus 5.8%, P = 0.0188), hypertensive disorder (17.6 versus 5.2%, P = 0.015), labour induction (33.3 versus 14.3%, P = 0.004) and Caesarean section delivery (58.8 versus 20.8%, P < 0.0001) were found among the primiparous mothers than the multiparous group. Neonatal outcome, however, was similar in both groups. We conclude that the primiparous mothers aged 40 years and above had more complicated antenatal and labour courses than multiparous mothers. On the other hand, the neonatal outcomes of two groups were comparable.

Key words: antepartum haemorrhage/Caesarean section/hypertension/maternal age/parity


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The confluence of a number of social and demographic trends for the past 2 decades has resulted in an increasing number of women becoming pregnant relatively late in their reproductive life. Although the final United States birth statistics for 1993 published by the National Center for Health Statistics reported the birth rate per 1000 total population at its lowest rate in 15 years, the number of births to women aged 35–39 years was higher than any year since 1960 (Ventura et al., 1995Go). Women older than 35 years have been referred to as of `advanced maternal age' or specifically as the `elderly' or `mature' pregnant woman (Kirz et al., 1985Go; Bobrowski and Bottoms, 1995Go). Traditionally, these women are believed to have more adverse pregnancy outcomes than younger pregnant women. In fact, the great majority of the medical literature concerning late childbearing relates to women between the ages of 35–40 years. However, many of these studies showed the pregnancy performance and neonatal outcome among the group of mothers aged >35 years are similar to those of younger age (Kirz et al., 1985Go; Ho et al., 1986Go). These findings therefore constitute a challenge to the current definition of advanced maternal age, which uses 35 years as the cut-off point with reference to the age-related effects on pregnancy outcome.

In the literature, mothers aged 40 years and above exhibited significant differences in early pregnancy loss, genetic disorders, hypertension, diabetes mellitus, antepartum haemorrhage, preterm delivery and Caesarean section delivery (Spellacy et al., 1986Go). Furthermore, adverse fetal outcome has been reported, which is largely due to the associated increased incidence of chromosomal problems and other significant malformations (Hook, 1981Go). The available data suggest that the risks that begin to accelerate after the age of 35 years become considerably greater and increase more rapidly after the age of 40 years. The birth rate for women aged 40–44 years, although much lower than rates for women between 15 and 39 years old, has increased by 56% between 1980–1993. Further, the total number of births in 1993 for women aged 40–44 years was the highest since 1968 (Ventura et al., 1995Go). Thus it would appear more appropriate for the delineation of a really high-risk group by increasing the age cut-off to 40 years in the definition of advanced maternal age. Nevertheless, the number of studies on the pregnancy outcome in mothers aged 40 years and above are few. Moreover, many of the previous studies of the influence of advancing maternal age on the outcome of pregnancy have evaluated multiple demographic variables (Grimes and Gross, 1981Go; Naeye, 1983Go; Kirz et al., 1985Go; Berkowitz et al., 1990Go; Edge and Laros, 1993; Bobrowski and Bottoms, 1995Go). Comparison of outcomes has largely focused on fetal aneuploidy (Hook, 1981Go), birth weight (Lee et al., 1988Go) and operative delivery rate (Martel, 1987). On the other hand, the overall pregnancy performance among this group of mothers has seldom been addressed, especially in relation to confounding factors such as parity.

In Hong Kong, in spite of the decreasing birth rate over the past 20 years (6.6% in 1977 versus 4.5% in 1992), the birth rate in the age group of 40–49 years old remained similar (1.0% in 1977 versus 1.2% in 1992). It implied that more women started to have their children at a later stage of their life (The Family Planning Association of Hong Kong, 1993Go). Since there are no data in an Asian population, a review of the obstetric performance with respect to parity of mothers older than 40 years in Hong Kong was therefore conducted. The results were expected to provide a better understanding of the pregnancy performance among older mothers and, in turn, assist in the preconception counselling of these women before conception and in their management during and after pregnancy.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Our hospital is a regional tertiary centre. In this retrospective study, the obstetric records of 205 women aged 40 or above who were delivered between January 1994 and December 1996 were reviewed. The following data, including maternal demographics (parity, height and pre-pregnant weight); antenatal complications (antepartum haemorrhage, hypertension, glucose intolerance, preterm delivery); labour performance (induction of labour, mode of delivery); and neonatal outcome (birth weight, Apgar scores, neonatal intensive care unit admission, perinatal mortality), were collected and compared with respect to parity. These data were also compared with data from mothers aged <40 years, with corresponding parity, who delivered in the same hospital during the same period. For this study, the cases that underwent therapeutic termination of pregnancy for lethal congenital anomalies and chromosomal disorders were excluded.

Antepartum haemorrhage was defined as vaginal bleeding complicating pregnancy after 28 completed gestational weeks. The main causes included abruptio placentae, placenta praevia, extra-uterine causes and of unknown origin. Hypertension in pregnancy was defined as either a diastolic blood pressure of >110 mm Hg on one occasion or a diastolic blood pressure of >90 mm Hg on two or more consecutive occasions >4 h apart. Gestational glucose intolerance was tested in every woman during the antenatal period through the implementation of a screening programme in Tsan Yuk Hospital. Patients who had risk factors for glucose intolerance, e.g. previous big babies, family history, maternal obesity, glycosuria and maternal age >35 years, previous unexplained stillbirth or abnormal babies, took a 75 g oral glucose tolerance test (OGTT) for screening. All other antenatal patients booked before 32 weeks were screened between 28 and 32 weeks gestation by spot sugar (venous blood) checking when they attended the antenatal clinic in Tsan Yuk Hospital during this gestational period. Patients with risk factors mentioned above who had a negative OGTT before had a repeat OGTT performed at 28–32 weeks. For patients who booked in after 32 weeks gestation, routine spot sugar screening was not performed. If there were clinical features suggestive of gestational glucose intolerance, or if they had risk factors as mentioned, they had the OGTT instead. The diagnosis for gestational diabetes mellitus was based on the World Health Organization criteria for diabetes mellitus (i.e. fasting plasma glucose level >8.0 mmol/l or 2 h plasma glucose level >11.0 mmol/l). Similarly, gestational impaired glucose tolerance refers to the same category of impaired glucose tolerance (i.e. fasting plasma glucose level <8.0 mmol/l and 2 h plasma glucose level = 8.0 to <11.0 mmol/l) in the WHO criteria. In this study, gestational diabetes mellitus and impaired glucose tolerance were analysed collectively as glucose intolerance.

Statistical analysis was performed using the {chi}2 test (with Yates' correction), Fisher's Exact test and t-test where appropriate. The differences were considered significant at the P < 0.05 level (two-tailed) and the odds ratio (OR) with 95% confidence interval was calculated.


    Results
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
A total of 205 records of women aged 40 years or more was reviewed. Among these, 51 (24.9%) mothers were primiparous and 154 (75.1%) mothers were multiparous. The age distribution with respect to parity is shown in Table IGo. There was no difference in the height (153.9 ± 6.1 versus 154.4 ± 5.8 cm) or the pre-pregnant weight (54.6 ± 7.5 kg versus 54.6 ± 7.5 kg) between the primiparous and multiparous mothers. Concerning obstetric history, primiparas had significantly less first trimester induced abortion than multiparas (Table IIGo). During the same period, 15 131 mothers aged <40 years delivered in our hospital, and the mothers aged 40 years or above accounted for 1.35% of the total deliveries.


View this table:
[in this window]
[in a new window]
 
Table I. Age distribution in mothers >40 years old
 

View this table:
[in this window]
[in a new window]
 
Table II. Antenatal complications, labour performance and neonatal outcome
 
The primiparous mothers had a higher incidence of antepartum haemorrhage (17.6 versus 5.8%, P = 0.02, OR = 3.452, 95% CI = 1.288–9.254) and hypertensive disorder (P = 0.015, OR = 3.911, 95% CI = 1.421–10.762) (Table IIGo). The subtypes of antepartum haemorrhage were presented. There was no statistically significant difference in the incidence of glucose intolerance between the primiparous and the multiparous groups. The mean (SD, range) gestational ages in primiparous and multiparous groups were 38.6 weeks (2.0, 29–41) and 38.6 weeks (1.6, 33–42) respectively. No significant difference was shown.

The rate of labour induction was significantly higher in the primiparous group (33.3 versus 14.3%, P = 0.004, OR = 3.000, 95% CI = 1.436–6.267) (Table IIGo). Similarly, the rate of Caesarean section delivery was significantly higher among the primiparous mothers (58.8 versus 20.8%, P < 0.0001, OR = 5.446, 95% CI = 2.759–10.753). The mean birthweights of the primiparous and multiparous groups were similar at 3180 g (SD = 586, 935–4405) and 3229 g (SD = 436, 1425–4355) respectively. There was no significant difference in the incidence of low birthweight (<2500 g) or macrosomia (>4000 g), or the incidence of low Apgar scores (<4) at both 1 and 5 min. The incidences of neonatal intensive care unit admission were similar and there was no perinatal death in both parity groups.

Compared with primiparas <40 years old, the primiparas >40 years old had increased incidence of antepartum haemorrhage, hypertension, glucose intolerance, induction of labour and Caesarean section (Table IIIGo). On the other hand, multiparas >40 years old only had increased incidences of glucose intolerance and Caesarean section (Table IVGo). There was no increased incidence of adverse perinatal outcome for both primiparas and multiparas >40 years old.


View this table:
[in this window]
[in a new window]
 
Table III. Comparison with younger primiparas
 

View this table:
[in this window]
[in a new window]
 
Table IV. Comparison with younger multiparas
 

    Discussion
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
In this retrospective study, in both primiparous and multiparous groups, the majority was aged 40 and 41 years and no significant difference was found in the age-parity distribution between two groups. The incidence of mothers aged 40 years and above in our study groups is similar to that in the Hong Kong population (1.5%) (Hong Kong College of Obstetricians and Gynaecologists, 1994) and Canada (1.19%) (Ananth et al., 1996Go). One primiparous mother conceived with the assistance of artificial insemination by her husband. All other mothers conceived spontaneously. The low incidence of post-assisted reproduction pregnancy may be due to the age limit of 35 years for the enrolment of assisted reproduction services in our unit.

Our results showed that the incidence of antepartum haemorrhage in the primiparous women was significantly higher than that in the multiparous group. Since we considered all subtypes of antepartum haemorrhage as a whole for the analysis because of small sample size, the impact of parity on individual causes of antepartum haemorrhage was not investigated separately. It may therefore mask certain information. For example, placenta praevia was known to be associated with multiparity, which is contradictory to our finding. Hypertension, one of the predisposing factors of antepartum haemorrhage, was also investigated. In this study, we have not subdivided the hypertensive disorder into pregnancy-induced hypertension, chronic hypertension with or without pre-existing renal disease, or unclassified hypertension for the analysis for the same reason as stated for antepartum haemorrhage. Similar to the younger primiparous, the elderly primiparous mothers also had a higher incidence of hypertensive disorders than the multiparous ones. This difference might have contributed to the higher incidence of antepartum haemorrhage in our primiparous mothers. In addition, the incidence of these two complications was also higher in the elderly primiparous mothers compared with the younger ones, suggesting that maternal age made a significant contribution to these complications. The incidence of glucose intolerance was similarly high for both parity groups for the elderly mothers. On the other hand, among the primiparous group, elderly mothers were associated with a higher incidence of glucose intolerance compared to younger mothers. This suggested that age imposed a more important effect on the incidence of glucose intolerance than parity. This age-related association, however, was not demonstrated in other obstetric complications.

Contrary to the literature, the incidence of preterm delivery among the primiparous mothers was similar to that among the multiparous.

In our series, the labour induction rate among the primiparous mothers was significantly higher than that among the multiparous group. Among the elderly primiparous mothers, because of the decreased fecundity and the probability of this being the only pregnancy, both patients and obstetricians tend to adopt a more active approach. This probably explains the higher labour induction rate. In addition, since certain obstetric complications, such as antepartum haemorrhage and hypertension, were more commonly found among the older primiparous mothers, this would have definitely increased the labour induction rate.

The criticism of liberal labour induction lies in the risk of iatrogenic fetal distress and the higher chance of operative delivery. In this study, the Caesarean section rate was significantly higher among the primiparous group than the multiparous one. Fetal distress constituted 40 (10/25) and 24.1% (7/29) of the indications for Caesarean section in primiparous and multiparous mothers respectively. On the other hand, 12 (3/25) and 3.4% (1/29) of the Caesarean sections in primiparous and multiparous mothers respectively were performed for failed induction. Statistical analysis was not performed because of the small sample size. Compared to younger mothers with respective parity, the difference in the Caesarean section rate persisted (Tables III and IVGoGo).

In spite of different antenatal and intrapartum performance, the neonatal outcomes were similar in the two parity groups. Although this could be due to different management approaches towards different parity groups, or due to inadequate power of the study related to the small sample size, a previous study has shown that there was no significant increase in both the perinatal mortality and morbidity in older compared to younger groups (Lagrew et al., 1996Go). It is likely that an adverse perinatal outcome was largely avoided due to the identification of this group of mothers as being high risk and they were therefore monitored closely and managed actively.

The results of this study suggest that although there were increased maternal risks in mothers aged 40 years and above, with the primiparous at higher risk, this was not associated with significantly increased perinatal risks, once the cases with fetal anomalies and therapeutic abortions were excluded. The different maternal risks cannot be explained by the previous history of first trimester-induced abortion, as the directions of differences were opposite. On the other hand, because of the low incidence of most obstetric complications and adverse outcome, a larger sample size may be needed to confirm our observations. Besides, retrospective studies may lead to sample selection bias. For example, in Hong Kong, older pregnant mothers with better financial status may elect to receive their obstetric care in private hospitals. This would mean that our patients may be representative only of the less affluent sector of the local population. If this was true, then the overall outcome may be even better. It is therefore likely that once pregnancies with fetal anomalies were terminated following prenatal screening, one could expect a more favourable obstetric outcome, so that pregnancy should not be contraindicated on the basis of age alone.


    Notes
 
3 To whom correspondence should be addressed Back


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Ananth, C.V. et al. (1996) Effect of maternal age and parity on the risk of uteroplacental bleeding disorders in pregnancy. Obstet. Gynecol., 88, 511–516[Abstract/Free Full Text]

Berkowitz, G.S., Skovron, M.L., Lapinski, R.H. et al. (1990) Delayed childbearing and the outcome of pregnancy. N. Engl. J. Med., 322, 659–664.[Abstract]

Bobrowski, R.A. and Bottoms, S.F. (1995) Underappreciated risks of elderly multipara. Am. J. Obstet. Gynecol., 172, 1764–1770.[ISI][Medline]

Edge, V. and Laros, R.K. Jr (1993) Pregnancy outcome in nulliparous women aged 35 or older. Am. J. Obstet. Gynecol., 168, 1881–1885.[ISI][Medline]

Grimes, D.A. and Gross, G.K. (1981) Pregnancy outcome in black women aged 35 or older. Obstet. Gynecol., 58, 614–620.[Abstract]

Ho, P.C., So, W.K. and Ma, H.K. (1986) Obstetric performance of elderly primiparae. Asian–Oceania J. Obstet. Gynaecol., 12, 499–504.

Hong Kong College of Obstetricians and Gynaecologists (1995) Territory-Wide Audit in Obstetrics & Gynaecology, Hong Kong, 1994.

Hook, E.B. (1981) Rates of chromosomal abnormalities at different maternal ages. Obstet. Gynecol., 58, 282–285.[Abstract]

Kirz, D.S., Dorchester, W. and Freeman, R.K. (1985) Advanced maternal age: the mature gravida. Am J. Obstet. Gynecol., 152, 7–12.[ISI][Medline]

Lagrew, D.C. Jr Margan, M.A., Nakamoto, K. et al. (1996) Advanced maternal age: perinatal outcome when controlling for physician selection. J. Perinatol., 16, 256–260.[Medline]

Lee, K., Ferguson, R.M., Corpuz, M. et al. (1988) Maternal age and incidence of low birth weight at term: a population study. Am. J. Obstet. Gynecol., 158, 84–89.[ISI][Medline]

Martel, M., Wacholder, S., Lippman, A. et al. (1987) Maternal age and primary cesarean rates: a multivariate analysis. Am. J. Obstet Gynecol., 156, 305–308.[ISI][Medline]

Naeye, R.L. (1983) Maternal age, obstetric complications, and the outcome of pregnancy. Obstet. Gynecol., 61, 210–216.[Abstract]

Spellacy, W.N., Miller, S.J. and Winegar, A. (1986) A pregnancy after 40 years of age. Obstet. Gynecol., 68, 452–454.[Abstract]

The Family Planning Association of Hong Kong (1993) Report on the Survey of Family Planning in Hong Kong 1992.

Ventura, S.J., Martin, J.A., Curtin, S.C. et al. (1995) Advanced report of final natality statistics, 1993. Monthly Vital Statistics Report, National Center for Health Statistics, 44, 1–88.

Submitted on June 11, 1998; accepted on November 20, 1998.