[1] St Georges Univ Hosp NHS Fdn Trust, Dept Obstet & Gynaecol, Fetal Med Unit, London SW17 0QT, England
[2] Middle East Tech Univ, Fac Arts & Sci, Dept Stat, Ankara, Turkey
[3] Koc Univ, Sch Med, Dept Obstet & Gynaecol, Istanbul, Turkey
[4] London Sch Hyg & Trop Med, Dept Hlth Serv Res & Policy, London, England
[5] Royal Coll Obstetricians & Gynaecologists, London, England
[6] Univ Coll London Hosp NHS Fdn Trust, London, England
[7] Norfolk & Norwich Univ Hosp NHS Fdn Trust, Norwich, Norfolk, England
[8] North Bristol NHS Trust Dept Womens Hlth, Westbury On Trym, England
[9] Univ Birmingham, WHO Collaborating Ctr Womens Hlth, Inst Metab & Syst Res, Birmingham, W Midlands, England
[10] St Georges Univ London, Inst Infect & Immun, Paediat Infect Dis Res Grp, London, England
[11] St Georges Univ London, Inst Infect & Immun, Vaccine Inst, London, England
[12] St Georges Univ London, Mol & Clin Sci Res Inst, Vasc Biol Res Ctr, London, England
[13] Publ Hlth England, Immunisat & Countermeasures Div, London, England
[14] Royal Coll Paediat & Child Hlth, British Paediat Surveillance Unit, London, England
[15] Kings Coll London, Sch Life Course Sci, Dept Women & Childrens Hlth, London, England