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Authors

  • Athol Kent


Caesarean section rates and cervical length

Caesarean section rates are highly dependent on the background caesarean section rate in any given population. Trends towards vaginal birth after caesarean section are slowing, so the primary caesarean section numbers strongly influence overall rates. Approximately 80% of primary intrapartum caesarean sections at term have poor progress in labour, with or without fetal distress as their indication. It is acknowledged that the threshold for diagnosis of fetal jeopardy is getting lower and lower, with nonreassuring cardiotocograph patterns increasingly justifying abdominal delivery.

The diagnosis of poor progress, failure to progress, dystocia or prolonged first stage is also very much at the discretion of the attending obstetrician but is usually made when cervical dilatation is slow in reaching the second stage. This mechanism is predicative on uterine contractions and cervical compliance, with the latter factor dependent both on the plasticity and on the length of the cervix at the initiation of labour. This favourability can be measured digitally or by ultrasound, and it seems that cervical length in midpregnancy can forecast the likelihood of a vaginal delivery at term or resort to caesarean section for dystocia.

The Second Trimester Screening Group in the UK performed transvaginal ultrasonic measurements on more than 25 000 primiparous women, which included the cervical length. The screening took place in midpregnancy and the researchers then related cervical length to the risk of a term caesarean section because of poor progress in labour (Smith et al., NEJM 2008;358:1346–53). They found the longer the cervix, the greater the risk of a caesarean section.

Women in the lowest quartile (16–30 mm) had a 16% caesarean section rate, while those in the highest quartile (40–67mm) had a 26% caesarean section rate, with a steady trend between the extremes. It is suggested that there is a relationship between dysfunctional development of the uterus in the second trimester and poor progress in labour, leading to increased rates of caesarean section at term.

Caesarean section information

Other aspects of caesarean delivery are being studied and the following summaries add to our knowledge on the procedure.

Exteriorisation of the uterus

Once the baby and placenta have been delivered, the uterine incision is sutured with the uterus either outside the abdominal cavity (exteriorised) or within the abdominal cavity (in situ). There are proponents of each method who claim that while exteriorisation allows better access to the incision and therefore faster stitching, the technique causes increased vagal stimulation and nausea. The suggestion of increased sepsis rates with exteriorisation has also been raised.

Continho et al. from Brazil randomly allocated more than 300 women into each arm of a randomised trial to compare exteriorisation with in situ repairs and found little difference in outcomes (Obstet Gynecol 2008;111:639–47). The exteriorised repairs were slightly quicker and used fewer sutures, but in situ suturing was associated with less postoperative pain at 6 hours. It seems surgical preference can dictate the technique as the differences are marginal in the real sense of the word.

Subsequent scar rupture

Vaginal birth after caesarean (VBAC) delivery was supported by those trying to reduce caesarean section rates, and in the USA over the past 30 years, VBAC rates have swung considerably. Reports of scar rupture risks have meant that initial rates (that rose from 3 to 30%) have now plateaued at 10%, but still within this group, it seems some situations are more vulnerable than others. Sciscione et al. (Obstet Gynecol 2008;111:648–53) have shown that women who had a previous preterm caesarean section are at twice the risk of rupture compared with those who had their previous caesarean section at term. The absolute risk remains small with an overall risk of 0.3%.

The authors postulate that the difference may be due to the physical differences of the lower segment formation earlier in pregnancy or the earlier deliveries being precipitated by inflammatory initiation of preterm delivery and, subsequently, poorer healing of the scar. The rupture is also more likely at an earlier gestational age, so this needs to be factored into the timing of elective surgery if that is decided upon.

Timing of elective caesarean section

The onset of labour is associated with improved neonatal lung function compared with infants delivered by elective caesarean section before labour, probably because of surges in catecholamines and steroids and changes in oxygen tension. The timing of elective caesarean sections is important in reducing the incidence of respiratory distress syndrome (RDS), but it seems that there are racial differences in lung maturation relative to gestational age.

Balchin et al. (Obstet Gynecol 2008;111:659–66) observed both earlier onsets of labour and reduced rates of RDS in women and infants of South Asian and black racial groups. They suggest that the 39 weeks optimal elective caesarean section timing for whites should be reduced to 38 weeks for South Asian and black women to strike an optimal balance between elective procedures being switched perforce to emergencies and the prevalence of RDS in their offspring.

Race and rupture

It seems that there are racial disparities in the predisposition of a previous caesarean section scar to rupture in a subsequent labour. Looking at a large cohort of women attempting a vaginal delivery after a caesarean section, Cahill et al. from the USA noted that black women were less likely to rupture their uterus than their white counterparts (Obstet Gynecol 2008;111:654–8).

This did not mean that their trial labour was more likely to end in a vaginal delivery (with the odds slightly against them) but knowing that their chances of rupture are 40% less than generally quoted for white women may materially affect decision-making.

IVF and acupuncture

In vitro conceptions now account for up to 4% of all pregnancies in developed countries. In Europe alone, some 300 000 treatment cycles are carried out per year, with 90% of them resulting in at least one embryo being transferred. The problem is that only about 25% of all cycles lead to implantation and a live birth.

Clearly, any means to improve the proportion of live births per cycle is attractive, both medically and commercially, and many have been tried—like using support gonadotrophins with luteinizing activity, assisted hatching and the transfer of 5-day rather than 3-day embryos. All these have their statistical advantages, but other factors such as cost and adverse effects have to be taken into account when deciding to incorporate them into standard practice.

An adjunct therapy that has been grabbing attention is acupuncture. Its use to regulate the reproductive cycle in women has been used in China for centuries, and Manheimer et al. (BMJ 2008;336:545–9) quote possible mechanisms for its mode of action. They also reviewed the world literature and have produced a meta-analysis, which suggests that, given with embryo transfer, acupuncture enhances a woman’s chances of pregnancy and a live birth. They calculate that ten women would need to be treated for an additional pregnancy and live birth. Whether these data are reproducible in large prospective trials is for the future, but the order of magnitude of improved outcomes is higher than more conventional adjunct manoeuvres, so some enthusiasts are likely to be persuaded by the evidence presented.

Normal early pregnancy

Women are encouraged to book in the first trimester, and usually, an ultrasound is carried out to confirm viability by the presence of cardiac activity. If the woman is low risk, she can be reassured that her chances of the pregnancy progressing are very good, but the actual statistics are unknown. Data from assisted reproduction programmes may not be the same for spontaneous conceptions, so Tong et al. (Obstet Gynecol 2008;111:710–14) worked out the odds of normal pregnancy miscarriage risk.

At 6 completed weeks of gestation, those women had a 91% chance of the pregnancy continuing past 20 weeks—that is, of not having a miscarriage. The chances of a successful outcome rose with each week, being 96% at 7 weeks, 98.5% at 8 weeks and over 99% for 9 and 10 weeks.

The figures are lower than the expected 15% of miscarriage rate of all clinically recognised pregnancies and obviously better than those presenting with complications, such as pain or bleeding. These data may be helpful to clinicians and prospective parents seeking reassurance before announcing their pregnancy.

There has been controversy over the implication of caffeine consumption in early pregnancy and the risk of miscarriage. Caffeine readily crosses the placenta so is a potential risk factor, but coffee ingestion has been linked with nausea and vomiting, which is associated with a decreased risk, making a confused picture. Wong et al. (AJOG 2008;198:278–81) conducted a survey of caffeine intake that took into account possible biases and showed that more than 200 mg of caffeine per day was linked to double the background miscarriage rate. It seems that there is sufficient evidence to advise women to curtail their consumption of caffeine-containing beverages in early pregnancy.

Intrauterine contraceptive devices

Intrauterine contraceptive devices (IUCDs) are used by more than 150 million women worldwide—mainly in developing countries. Since these are the nations bearing the greatest burden of disease and facing the largest population growth rates, IUCDs can be described as holding the key to the planet’s future.

Their limited uptake in Europe and USA seems anomalous, given the upbeat review by Thonneau and Almont (AJOG 2008;198:248–53) revealing overall 5-year pregnancy rates of less than 2% with very much lower rates for the levonorgestrel-releasing and certain copper-containing devices. These figures are comparable with oral contraceptive rates over time and have the advantages of cost, continuity, discretion and distribution.

Advances with the frameless systems, where thin copper tubes are threaded over nonabsorbable strands, are being researched. If the device is correctly anchored to the fundus, the system works very well, but it seems skilled insertion is a key feature.

It is interesting to note that the review does not mention any association between IUCDs and infection, so perhaps this ghost has been put to rest.

Sexual function after menopause

Sexual dysfunction after the menopause is common and presumed to be caused by decreased estrogen levels. In particular, vaginal pain and dryness are quoted as troublesome, so treatment with estrogen replacement seems logical.

Huang et al. (AJOG 2008;198:265–7) studied the effects of an ultra low-dose estrogen-only patch on a group of postmenopausal women with a mean age of 67 years and noted a modest improvement in symptoms compared with placebo. It did not affect other aspects of sexual function, such as libido, arousal or frequency of intercourse. These findings were independent of baseline hormone levels, and treatment was not associated with bleeding of any description.

Footnotes

  1. These snippets are extracts from a monthly service called the Journal Article Summary Service. It is a service that summarises all that is new in obstetrics and gynaecology over the preceding month. If you would like to know the details of how to subscribe, please email the editor Athol Kent at atholkent@mweb.co.za or visit the website http://www.jassonline.com/.

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