It’s not just the size, but also the gestational age that determine survival. In addition, the level hospital of birth plays a big part. If you give birth at a regional center equipped with a full NICU (neonatal intensive care unit), you will fare much better.
In general, 25–26 weeks gestation have >80% survival rates. 23 weeks gestation with a birth weight 500–699g has under 50% survival, but >700g has over 50%. 24 weeks gestation is in-between the two.
As @ANef_is_Enuf mentioned, this is only survival, not morbidity. Morbidity will depend on gestational age and birth weight (and level of hospital of birth) as well, but will also depend on infections, oxygenation (too much or too little), feeding/intestinal issues, etc.
Feel free to PM me. I’m a neonatal clinical data analyst.