Second tier non-invasive prenatal testing in a regional prenatal diagnosis service unit: a retrospective analysis and literature review

INTRODUCTION

The Hong Kong Hospital Authority has newly introduced a new Down's syndrome screening algorithm that offers free-of-charge non-invasive prenatal testing (NIPT) to women who screen as high risk. In preparation for this public-funded second tier NIPT service, the present study was conducted to retrospectively analyse women eligible for NIPT and to review the local literature.

METHODS

Our retrospective study included women screened as high risk for Down's syndrome (adjusted term risk ≥1:250) during the period of 1 January 2015 to 31 December 2016. We performed descriptive statistics and multivariable logistic regression to examine the factors associated with women's choice between NIPT and invasive testing. We also reviewed existing local literature about second tier NIPT.

RESULTS

The study included 525 women who screened positive: 67% chose NIPT; 31% chose invasive diagnostic tests; and 2% declined further testing. Our literature review showed that in non-research (self-financed NIPT) settings, NIPT uptake rates have been increasing since 2011. Nulliparity, first trimester status, higher education, maternal employment, and conception by assisted reproductive technology are common factors associated with self-financed NIPT after positive screening. Among women choosing NIPT, the rates of abnormal results have typically been around 8% in studies performed in Hong Kong.

CONCLUSION

Implementation of second tier NIPT in the public setting is believed to be able to improve quality of care. We expect that the public in Hong Kong will welcome the new policy.

Pattern and predictors of medical care received by hepatitis B carriers during pregnancy and after delivery

OBJECTIVE

The objective of the study is to evaluate the pattern and predictors of medical care received by hepatitis B virus (HBV) carriers during pregnancy and after delivery in Hong Kong.

STUDY DESIGN

The study is a retrospective analysis.

METHODS

Pregnant HBV carriers and their infants were followed up for 9-12 months after delivery. Face-to-face interviews were conducted to investigate what medical care they received for HBV before, during and after pregnancy.

RESULTS

Data were available for 412 HBV carriers. A total of 375 (91.0%) women were known HBV carriers before pregnancy. Routine antenatal screening picked out the remaining 37 (9.0%) HBV carriers; these women were younger, more likely to be smokers and had a lower level of education (P < 0.05) than known HBV carriers. In total, 356 of 412 (86.4%) HBV carriers did not receive any medical care for HBV during pregnancy. Known HBV carrier status, history of medical check-up and the use of antiviral treatment before pregnancy were significant predictors for HBV medical care during pregnancy (P < 0.05). The results show that 217 of 412 (52.6%) HBV carriers did not receive medical care for HBV after delivery. HBV medical care before pregnancy, use of antiviral treatment before pregnancy and a higher level of education were significant predictors for postpartum HBV medical care (P < 0.05). Multivariate analysis showed that HBV medical care before pregnancy (odds ratio [OR], 7.73; 95% confidence interval [CI], 3.21-18.65; P < 0.001) and the use of antiviral treatment (OR, 5.02; 95% CI, 1.41-17.81; P = 0.013) were associated with medical care during pregnancy. Medical care before pregnancy was also associated with postpartum HBV medical care (OR, 5.05; 95% CI, 3.29-7.51; P < 0.001).

CONCLUSIONS

A significant proportion of HBV carriers did not receive HBV-related medical check-ups during and after pregnancy in Hong Kong despite the majority being aware of their carrier status. Medical care before pregnancy predicted antenatal and postpartum HBV medical care.

Indications for and pregnancy outcomes of cervical cerclage: 11-year comparison of patients undergoing history-indicated, ultrasound-indicated, or rescue cerclage

OBJECTIVES

To review and compare pregnancy outcomes of patients undergoing history-indicated, ultrasound-indicated, or rescue cerclage.

DESIGN

Case series with internal comparison.

SETTING

A regional obstetric unit in Hong Kong.

PATIENTS

Women undergoing cervical cerclage at Kwong Wah Hospital between 1 January 2001 and 31 December 2011.

INTERVENTIONS

Cervical cerclage.

MAIN OUTCOME MEASURES

Pregnancy outcomes including miscarriage, gestational age at delivery, birth weight, and duration of pregnancy prolongation.

RESULTS

Overall, 47 patients were included. Nine (19.1%) pregnancies resulted in miscarriage. The median gestational age at delivery was 35.7 weeks. Among the 23 patients who had history-indicated cerclage, only four (17.4%) had three or more previous second-trimester miscarriages or preterm deliveries. Among the 15 patients who had ultrasound-indicated cerclage, preoperative cervical length of ≤1.5 cm was associated with shorter prolongation of pregnancy, compared with that of >1.5 cm (median, 12.1 vs 18.4 weeks; P=0.009). Among the nine women who had rescue cerclage, those who underwent the procedure before 20 weeks of gestation delivered earlier than those underwent cerclage later (median, 22.5 vs 34.1 weeks; P=0.048).

CONCLUSIONS

Patients eligible for the Royal College of Obstetricians and Gynaecologists-recommended history-indicated cerclage remain few. The majority of patients may benefit from serial ultrasound monitoring of cervical length with or without ultrasound-indicated cerclage.

Social obstetrics: non-local expectant mothers admitted through accident and emergency department in a public hospital in Hong Kong

OBJECTIVES

To review the pregnancy outcomes of non-booked, non-local pregnant women delivering in Kwong Wah Hospital via admission to the Accident and Emergency Department 1 year after the announcement by the Hospital Authority to stop antenatal booking for non-eligible persons; and to perform a literature review of local studies about non-eligible person deliveries over the last decade.

DESIGN

Case series.

SETTING

A public hospital in Hong Kong.

PARTICIPANTS

All women who held the People's Republic of China passport or the two-way permit and those non-eligible persons whose spouses were Hong Kong Identity Card holders, who delivered in Kwong Wah Hospital from 1 April 2011 to 31 March 2012.

RESULTS

Overall, 219 women who were non-eligible persons delivered 221 live births during the study period. Compared with the annual statistics of Kwong Wah Hospital in 2011, non-local mothers were of higher parity; more likely to have hypertensive disease (including pre-eclamptic toxaemia), preterm deliveries (ie at <37 weeks), babies needing admission to the special care baby unit, and macrosomic babies (ie weighing >4.0 kg). The rates of induction of labour and caesarean section were lower in this group. There was no significant difference in the maternal and neonatal outcomes between women who had no booking and those who had a booking in another Hospital Authority or private hospital. There were many incidents of near-miss obstetric complications or suboptimally managed obstetric conditions due to lack of well-structured and continuous antenatal care in this group of non-eligible persons.

CONCLUSION

Non-eligible person delivering babies in Hong Kong has become a social obstetrics phenomenon. Despite the introduction of policies, reduction in the number of deliveries (quantity) did not improve the obstetric outcomes (quality). Health care professionals should continue to be prepared for managing the potential near-miss clinical complications in this group of 'travelling mothers'.

Planned conservative management of placenta accreta - experience of a regional general hospital

OBJECTIVE

There are only a few series treating ≥10 cases of accreta conservatively, all from university teaching hospitals, with reported success rate of 60-85%. We reported the first series of accreta managed by planned uterine conservation in the setting of non-university district general hospital.

METHODS

Women with placenta previa overlying previous cesarean scar who desired uterine conservation were included. For cases with accreta confirmed during cesarean delivery, placenta was purposefully left behind, followed immediately by uterine artery embolization. Cases were followed in our special postnatal clinic. Charts were reviewed to retrieve clinical details.

RESULTS

Among 15 cases of placenta previa overlying cesarean scar opting for conservative management, 12 (80%) were confirmed to be accreta intra-operatively. They had 20-100% of the adherent placentae retained (median 90%) and their uterus preserved. Postpartum, abnormal vaginal bleeding and/or infection led to unscheduled readmission in 67% (8/12), all managed conservatively. Sonographic resolution of placenta took 2-13 months (median 6.6), and was later than menstrual return in 11 cases.

CONCLUSIONS

Successful planned conservative management of placenta accreta is feasible in the setting of district general hospital with facilities for interventional radiology.

Intensive care unit admission of obstetric cases: a single centre experience with contemporary update

OBJECTIVES. To review the characteristics of a series of obstetric patients admitted to the intensive care unit in a regional hospital in 2006-2010, to compare them with those of a similar series reported from the same hospital in 1989-1995 and a series reported from another regional hospital in 1998-2007. DESIGN. Retrospective case series. SETTING. A regional hospital in Hong Kong. PATIENTS. Obstetric patients admitted to the Intensive Care Unit of Kwong Wah Hospital from 1 January 2006 to 31 December 2010. RESULTS. From 2006 to 2010, there were 67 such patients admitted to the intensive care unit (0.23% of total maternities and 2.34% of total intensive care unit admission), which was a higher incidence than reported in two other local studies. As in the latter studies, the majority were admitted postpartum (n=65, 97%), with postpartum haemorrhage (n=39, 58%) being the commonest cause followed by pre-eclampsia/eclampsia (n=17, 25%). In the current study, significantly more patients had had elective caesarean sections for placenta praevia but fewer had had a hysterectomy. The duration of intensive care unit stay was shorter (mean, 1.8 days) with fewer invasive procedures performed than in the two previous studies, but maternal and neonatal mortality was similar (3% and 6%, respectively). CONCLUSION. Postpartum haemorrhage and pregnancy-induced hypertension were still the most common reasons for intensive care unit admission. There was an increasing trend of intensive care unit admissions following elective caesarean section for placenta praevia and for early aggressive intervention of pre-eclampsia. Maternal mortality remained low but had not decreased. The intensive care unit admission rate by itself might not be a helpful indicator of obstetric performance.

Factors influencing the mode of delivery and associated pregnancy outcomes for twins: a retrospective cohort study in a public hospital

OBJECTIVES

To determine current trends for different modes of delivery in twin pregnancies, factors affecting the mode of delivery, and associated outcomes.

DESIGN

Retrospective cohort study.

SETTING

A public hospital in Hong Kong.

PARTICIPANTS

All twin pregnancies booked at Kwong Wah Hospital during a 3-year period from 1 April 2006 to 31 March 2009.

RESULTS

Of 197 sets of twins, 35 (18%) were delivered vaginally and 162 (82%) by caesarean section (47% were emergencies and 53% elective). In all, 32 (37%) of the elective and 21 (28%) of the emergency caesarean sections were in response to maternal requests. Vaginal delivery was more common in mothers with a history of vaginal delivery and monochorionic diamniotic twins. Women who conceived by assisted reproduction or those who had a tertiary education were more likely to deliver by caesarean section. The type of conception and the presentation of the second twin were statistically significant factors affecting maternal choice on the mode of delivery. Maternal age did not affect the choice of delivery mode. Except for the higher frequency of sepsis and cord blood acidosis in second twins delivered vaginally, there were no significant differences in neonatal morbidity between the groups that attempted vaginal delivery or requested caesarean sections. All the women who had compression sutures or hysterectomy to control massive postpartum haemorrhage were delivered by caesarean section.

CONCLUSION

A high caesarean section rate observed in our cohort was associated with maternal requests for this mode of delivery. The type of conception and the presentation of the second twin were statistically significant factors affecting maternal choice on mode of delivery. Women's requests for caesarean delivery out of the concern for their babies are not supported by current evidence. In response to a woman with a twin pregnancy requesting caesarean delivery, the pros and cons of vaginal deliveries and caesarean sections should be fully explained before the woman's autonomy is respected.

Predictors of successful outcomes after external cephalic version in singleton term breech pregnancies: a nine-year historical cohort study

OBJECTIVE

To study the success rate, predictors for success, and pregnancy outcomes after external cephalic version.

DESIGN

Historical cohort study.

SETTING

Regional hospital, Hong Kong.

PATIENTS

All women who had singleton term breech pregnancies at term and opted for external cephalic version during 2001 and 2009. Their demographic data, clinical and ultrasound findings, procedure details, complications, and delivery outcomes were analysed.

MAIN OUTCOME MEASURES

Predictive factors for successful external cephalic version.

RESULTS

A total of 209 external cephalic versions were performed during the 9-year period. The success rate was 63% (75% for multiparous and 53% for nulliparous women). There was no significant complication. On univariate analysis, predictors of successful external cephalic version were: multiparity, unengaged presenting part, higher amniotic fluid index (≥ 10 cm), thin abdominal wall, low uterine tone, and easily palpable fetal head (subjective assessment by practitioners before external cephalic version). On multivariate analysis, only multiparity, non-engagement of the fetal buttock and thin maternal abdomen were associated with successful external cephalic version. In all, 69% of those who had successful external cephalic version succeeded in the first roll (P<0.001), and 82% of the women with successful external cephalic versions had vaginal deliveries (93% in multiparous and 69% in nulliparous women). Uptake rate of external cephalic version was studied in the latter part of the study period (2006-2009). Whilst 735 women were eligible for external cephalic version, 131 women chose to have the procedure resulting in an uptake rate of 18%.

CONCLUSION

External cephalic version was effective in reducing breech presentations at term and corresponding caesarean section rates, but the uptake rate was low. Further work should address the barriers to the low acceptance of external cephalic version. The results of this study could encourage women to opt for external cephalic version.

Rapid aneuploidy testing (knowing less) versus traditional karyotyping (knowing more) for advanced maternal age: what would be missed, who should decide?

OBJECTIVES

The application of rapid aneuploidy testing as a stand-alone approach in prenatal diagnosis is much debated. The major criticism of this targeted approach is that it will not detect other chromosomal abnormalities that will be picked up by traditional karyotyping. This study aimed to study the nature of such chromosomal abnormalities and whether parents would choose to terminate affected pregnancies.

DESIGN

Retrospective study on a cytogenetic database.

SETTING

Eight public hospitals in Hong Kong.

PARTICIPANTS

The karyotype results of 19 517 amniotic fluid cultures performed for advanced maternal age (>or=35 years) from 1997 to 2002 were classified according to whether they were detectable by rapid aneuploidy testing. The outcomes of pregnancies with abnormal karyotypes were reviewed from patient records.

RESULTS

In all, 333 (1.7%) amniotic fluid cultures yielded abnormal karyotypes; 175 (52.6%) of these were detected by rapid aneuploidy testing, and included trisomy 21 (n=94, 28.2%), trisomy 18 or 13 (n=21, 6.3%), and sex chromosome abnormalities (n=60, 18.0%). The other 158 (47.4%) chromosomal abnormalities were not detectable by rapid aneuploidy testing, of which 63 (18.9%) were regarded to be of potential clinical significance and 95 (28.5%) of no clinical significance. Pregnancy outcomes in 327/333 (98.2%) of these patients were retrieved. In total, 143 (42.9%) of these pregnancies were terminated: 93/94 (98.9%) for trisomy 21, 20/21 (95.2%) for trisomy 18 or 13, 19/60 (31.7%) for sex chromosome abnormalities, and 11/63 (17.5%) for other chromosomal abnormalities with potential clinical significance. There were no terminations in the 95 pregnancies in which karyotyping results were regarded to be of no clinical significance.

CONCLUSIONS

'Knowing less' by the rapid aneuploidy stand-alone testing could miss about half of all chromosomal abnormalities detectable by amniocentesis performed for advanced maternal age. Findings from two fifths of the latter were of potential clinical significance, and the parents chose to terminate one out of six of the corresponding pregnancies. If both techniques are available, parents could have enhanced autonomy to choose.

Obstetric cholestasis in Hong Kong--local experience with eight consecutive cases

Obstetric cholestasis is associated with maternal morbidity and adverse foetal outcomes. No information on local incidence is available. We present our experience with eight consecutive cases of obstetric cholestasis diagnosed between January 2003 and December 2005 in a regional hospital in Hong Kong. Three patients presented with pruritus without rash, three with impaired liver function, and two with elevated blood pressure postpartum. Meconium-stained liquor was present in five patients and four had spontaneous preterm delivery (between 34 and 36 weeks). The higher the bile acid level, the more marked the prematurity (correlation coefficient, -0.771; P=0.025). All those presenting with itchiness delivered preterm. Two patients developed pre-eclampsia. The rates of labour induction and abdominal delivery were both 38%. Heightened awareness among clinicians is required to recognise patients with obstetric cholestasis. Affected pregnancies are associated with meconium passage and prematurity. In our locality, affected women may also have an increased risk of pre-eclampsia. In affected women, the bile acid level is useful in assessing the risk of prematurity.

Two cases of postmaturity-related perinatal mortality in non-local expectant mothers

We present two cases of postmaturity-related perinatal mortality with delivery at 42 weeks 6 days' and 44 weeks' gestation, respectively. No cause beyond postmaturity was found. Neither induction of labour nor foetal monitoring had been performed despite these gestations going post 41 weeks because of a current 'social obstetrics' phenomenon--non-local expectant mothers coming to Hong Kong from mainland China for delivery.

Reversed diastolic flow in the uterine artery - a new Doppler finding related to placental insufficiency?

Increased uterine artery pulsatility and resistance indices with or without notching of the waveform have been associated with an increased risk of pre-eclampsia and fetal growth restriction. However, reversed diastolic flow in the uterine artery has not previously been reported. We present two high-risk obstetric cases complicated by severe placental insufficiency: pre-eclampsia followed by eclampsia in one case and intrauterine growth restriction with abnormal cardiotocography in the other. Doppler studies of the uterine arteries revealed reversed diastolic flow in both cases. The pathophysiology and potential implications are discussed.

Sublingual misoprostol compared to artificial rupture of membranes plus oxytocin infusion for labour induction in nulliparous women with a favourable cervix at term

OBJECTIVES

To compare the efficacy of labour induction using sublingual misoprostol versus combined artificial rupture of membranes and oxytocin infusion for nulliparous women with a favourable cervix at term.

DESIGN

Open randomised controlled trial.

SETTING

Regional hospital, Hong Kong.

PATIENTS

Fifty nulliparous women with a favourable cervix (Bishop score 6 or more) at term and indications for labour induction.

INTERVENTIONS

With their informed consent, 100 eligible women were to be randomised to receive either sublingual misoprostol 50 micrograms every 4 hours for up to five doses or oxytocin infusion after artificial rupture of membranes. Interim analysis was planned at a sample size of 50.

MAIN OUTCOME MEASURES

Vaginal delivery within 24 hours of induction.

RESULTS

The study was terminated when interim analysis of the first 50 recruits showed that a significantly smaller proportion of misoprostol-treated women delivered vaginally within 24 hours of induction than in the conventional treatment group (68% vs 100%; relative risk, 0.68; 95% confidence interval, 0.51-0.91; P=0.009), although comparable numbers of women eventually delivered vaginally. The mean induction to vaginal delivery interval was 4.5 hours longer in the misoprostol group (P=0.027). After misoprostol treatment, all women went into labour. Forty percent of them delivered without oxytocin. There was no significant difference in uterine hyperstimulation rate, operative delivery rate, and neonatal outcomes. Maternal satisfaction was higher in the misoprostol group (92% vs 60%; relative risk, 1.53; 95% confidence interval, 1.09-2.16; P=0.008).

CONCLUSIONS

Despite being well accepted by women, labour induction using this regimen of sublingual misoprostol is less effective in achieving vaginal delivery within 24 hours.

Use of developmental language scales in Chinese children

The Reynell Developmental Language Scale (RDLS) and Symbolic Play Test (SPT) have been useful language tests for assessing the language age of children. Both tests have been validated in English-speaking children. However, there have been no studies conducted for Chinese children, whether Mandarin (Northerners) or Cantonese (Southerners) is used as the main dialect. As the Chinese population is the largest ethnic group in the world, and Chinese emigration occurred to nearly all parts of the world, it is essential to test whether these language tools can be applied for this ethnic group. The objective of this research was to study whether RDLS and SPT are useful in assessing the language age of Chinese children. Both RDLS (Chinese version) and SPT are conducted for 116 Chinese (Cantonese-speaking) children, aged 13-59 months, in Hong Kong. There is a significant positive correlation of the language age using RDLS and SPT with the chronological age of Chinese children. Both RDLS and SPT can be adopted in determining the language/mental age of Chinese (Cantonese-speaking) children.

Preliminary measurements of aromatic VOCs in public transportation modes in Guangzhou, China

This study examined the exposure level of aromatic volatile organic compounds (VOCs) in public transportation modes in Guangzhou, China. A total of 40 VOC samples were conducted in four popular public commuting modes (subway, taxis, non-air-conditioned buses and air-conditioned buses) while traversing in urban areas of Guangzhou. Traffic-related VOCs (benzene, toluene, ethylbenzene, m/p-xylene and o-xylene) were collected on adsorbent tubes and analyzed by thermal desorption (TD) and gas chromatography/mass-selective detector (GC/MSD) technique. The results indicate that commuter exposure to VOCs is greatly influenced by the choice of public transport. For the benzene measured, the mean exposure level in taxis (33.6 microg/m(3)) was the highest and was followed by air-conditioned buses (13.5 microg/m(3)) and non-air-conditioned buses (11.3 microg/m(3)). The exposure level in the subway (7.6 microg/m(3)) is clearly lower than that in roadway transports. The inter-microenvironment variations of other target compounds were similar to that of benzene. The target VOCs were well correlated to each other in all the measured transports. The concentration profile of the measured transport was also investigated and was found to be similar to each other. Based on the experiment results, the average B/T/E/X found in this study was about (1.0/4.3/0.7/1.4). In this study, the VOC levels measured in evening peak hours were only slightly higher than those in afternoon non-peak hours. This is due to the insignificant change of traffic volume on the measured routes between these two set times. The out-dated vehicle emission controls and slow-moving traffic conditions may be the major reasons leading elevated in-vehicle exposure level in some public commuting journeys.

Selective foeticide in Hong Kong-lawful or not?

There is legal uncertainty as to whether selective foeticide is authorised under section 47A of the Offences Against the Person Ordinance (1967). Medical and legal issues surrounding a case of selective foeticide in a triplet pregnancy are reported.

Dynamics and folding of single two-stranded coiled-coil peptides studied by fluorescent energy transfer confocal microscopy

We report single-molecule measurements on the folding and unfolding conformational equilibrium distributions and dynamics of a disulfide crosslinked version of the two-stranded coiled coil from GCN4. The peptide has a fluorescent donor and acceptor at the N termini of its two chains and a Cys disulfide near its C terminus. Thus, folding brings the two N termini of the two chains close together, resulting in an enhancement of fluorescent resonant energy transfer. End-to-end distance distributions have thus been characterized under conditions where the peptide is nearly fully folded (0 M urea), unfolded (7.4 M urea), and in dynamic exchange between folded and unfolded states (3.0 M urea). The distributions have been compared for the peptide freely diffusing in solution and deposited onto aminopropyl silanized glass. As the urea concentration is increased, the mean end-to-end distance shifts to longer distances both in free solution and on the modified surface. The widths of these distributions indicate that the molecules are undergoing millisecond conformational fluctuations. Under all three conditions, these fluctuations gave nonexponential correlations on 1- to 100-ms time scale. A component of the correlation decay that was sensitive to the concentration of urea corresponded to that measured by bulk relaxation kinetics. The trajectories provided effective intramolecular diffusion coefficients as a function of the end-to-end distances for the folded and unfolded states. Single-molecule folding studies provide information concerning the distributions of conformational states in the folded, unfolded, and dynamically interconverting states.

Synthesis, structure-activity relationships, and the effect of polyethylene glycol on inhibitors of phosphatidylinositol-specific phospholipase C from Bacillus cereus

Substrate analog inhibitors of Bacillus cereus phosphatidylinositol-specific phospholipase C (PI-PLC) were synthesized and screened for their suitability to map the active site region of the enzyme by protein crystallography. Analogs of the natural substrate phosphatidylinositol (PI) were designed to examine the importance of the lipid portion and the inositol phosphate head group for binding to the enzyme. The synthetic compounds contained pentyl, hexyl, or hexanoyl and octyl lipid chains at the sn-1 and sn-2 positions of the glycerol backbone and phosphonoinositol, phosphonic acid, methyl phosphonate, phosphatidic acid, or methyl phosphate at the sn-3 position. The most hydrophobic compound, dioctyl methyl phosphate 14, was also the best inhibitor with an IC50 of 12 microM. In a series of dihexyl lipids, compounds with phosphonoinositol head groups inhibited more strongly than those that do not contain inositol but are otherwise identical. Compound 29, a short-chain lipid with a phosphonoinositol head group, was found to be a competitive inhibitor and the most potent in this series with an IC50 of 18 microM (Ki = 14 microM). Analogs with dihexyl chains were better inhibitors than those with dihexanoyl chains, presumably because the ether-linked lipids are more hydrophobic than the ester-linked lipids. No appreciable difference in inhibition was found between a phosphonoinositol lipid and the corresponding difluorophosphonoinositol lipid. Inositols and inositol derivatives that do not contain lipid moieties show IC50s about 3 orders of magnitude above those of the short-chain lipids. In this group, glucosaminyl(alpha 1-->6)-D-myo-inositol inhibited more strongly than myo-inositol, which in turn is a better inhibitor than inositol phosphate. The addition of polyethylene glycol (PEG-600) resulted in a marked decrease in inhibition by the short-chain lipids, but had little effect on the water-soluble head group analogs. This is accounted for in terms of solubilization of the amphipathic inhibitors by PEG. Since PEG is required in the crystallization, these data indicate that the best strategy for obtaining enzyme inhibitor complexes is to start by cocrystallizing PI-PLC with the head group analogs. The next step is to synthetically add the shortest possible hydrophobic moieties to the analogs and cocrystallize these with the enzyme. This strategy may be applicable to other lipolytic enzymes.