Hindi ka mag-alala ma, 16 cm sounds small kaya better to get a second opinion from your pedia or OB to make sure everything's on track, pero ang midwife mo naman nagsabi it's okay for her age so that's reassuring! A few of us moms have had babies na parang maliit din at nag-catch up naman eventually, pero talaga di ako makapag-compare ng exact measurements kasi bawat baby talaga ang timeline eh. Since you already asked your midwife and she gave the okay, just keep monitoring with regular check-ups, pero if you're really worried, mas better mag-consult ulit with your doctor para peace of mind mo.