2 The technology

Description of the technology

2.1 The Vision Amniotic Leak Detector (ALD; CommonSense Ltd) is a non-invasive diagnostic panty liner that can be attached to underwear. The panty liner has a central polymer-embedded strip that turns blue-green on contact with fluid that has a pH higher than 5.2 (normal vaginal pH is 3.5 to 4.5 and amniotic fluid has a pH of 6.5 or above). The device can distinguish between amniotic fluid and urine (which contains ammonia) because the polymer strip contains reagents that react differently depending on the pH and whether ammonia is present. The presence of vaginal infection, including bacterial vaginosis, trichomoniasis or desquamative inflammatory vaginitis, can also produce a positive result because infection can raise vaginal pH. The Vision ALD is supplied in individually sealed packs, each containing a liner, a plastic drying unit and an instruction leaflet.

2.2 The liner should be worn until it is sufficiently wet for a result to be read, and for no longer than 12 hours. The indicator strip is then removed and placed in the drying unit for 30 minutes. If the indicator strip is yellow after drying, then the leak is unlikely to be amniotic fluid and a speculum examination can be avoided. If the indicator strip is blue-green after drying, this indicates the wetness is likely to be amniotic fluid or infection, which can be confirmed by a speculum examination and a vaginal swab.

2.3 The Vision ALD is intended for use by women with normal pregnancies experiencing unexplained vaginal wetness as well as by those at high risk of premature rupture of membranes.

2.4 The cost of the Vision ALD stated in the sponsor's submission is £1.60 per test.

2.5 The claimed benefits of Vision ALD in the case for adoption presented by the sponsor are:

  • A reduction in unnecessary speculum examinations.

  • A reduction in the time spent in hospital. Those who currently undergo a speculum examination need to remain in hospital for approximately 30 minutes pre-procedure and 45–60 minutes in total. Women using the Vision ALD will not require a hospital bed and can undergo the test as an outpatient or in a community setting; there is no requirement for them to lie down whilst wearing the liner.

  • A reduced risk of infection from speculum examination, particularly if repeat examinations are required.

  • The incidental detection of possible vaginal infection.

  • A reduction in the costs associated with the avoidance of speculum examination.

  • A reduction in staff time and hospital bed use.

Current management

2.6 Intrapartum care (NICE clinical guideline 55) indicates that a speculum examination should be used to detect ruptured amniotic membranes when any uncertainty exists. Expert advice suggests that the woman needs to lie down for up to 30 minutes before the procedure, so that any leaking amniotic fluid can collect in the vagina. After this time, a doctor or midwife will use a speculum to examine the vagina for pooling of amniotic fluid. If pooling is seen, the woman is diagnosed with ruptured membranes and her condition managed accordingly. If there is no pooling, it is assumed that the membranes are still intact and the woman may be discharged. Nitrazine (pH) testing, amniotic fluid crystallisation (fern testing), biomarker testing or ultrasound examination of the uterus may be used to confirm the diagnosis, but none of these are used routinely in the NHS as standard practice.

2.7 If membrane rupture is confirmed in women with pregnancies over 37 weeks' gestation (prelabour rupture of membranes [PROM]), the NICE clinical guideline on intrapartum care recommends that women should be given advice on the increased risk of neonatal infection and the probability of progression to labour. Induction is advised if labour has not started within 24 hours. Women can choose to continue with expectant management in hospital or at home. The fetus should be monitored every 24 hours and women asked to look for any signs of infection or changes in fetal movement. Intravenous antibiotics should be administered if signs of infection are present. After labour, women are asked to look for any signs of infection in their baby.

2.8 In the case of pregnancies under 37 weeks' gestation (preterm prelabour rupture of membranes [PPROM]), guidance from the Royal College of Obstetricians and Gynaecologists (2006) recommends that women should be monitored in hospital for at least 48 hours for signs of chorioamnionitis. Corticosteroids and erythromycin should be given. Some women can be monitored at home after 48 hours in hospital, but this decision depends on the individual woman's level of risk. Women are asked to monitor themselves for any signs of infection and return to hospital if this is suspected. Induction of labour should be considered after 34 weeks' gestation.

  • National Institute for Health and Care Excellence (NICE)