tubal less effective after birth?

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i’m 6 weeks postpartum and scheduled an appointment to see about getting my tubes tied. i had to go to a different office than my usual OB because the hospital closest to me doesn’t do them since it’s a catholic hospital… but the doctor said it’s less effective this soon after giving birth and to wait 4-5 months. i tried to google it and couldn’t find anything - is this true?

it’s just weird to me because i know they can be done during c sections. i just hate birth control and really wanted to avoid it 😭😭😭😭