Chemical abnormalities
Methemoglobinemia:
a condition caused by elevated levels of methemoglobin in the blood. Methaemoglobin is a form of Hb that contains the ferric [Fe3+] form of iron. The affinity for oxygen of ferric iron is impaired. The binding of oxygen to methaemoglobin results in an increased affinity for oxygen in the remaining heme sites that are in ferrous state within the same tetrameric haemoglobin unit. B)  Quantitative
Production abnormalities
Copy number variation (e.g., deletion, duplication, insertion) is also a common genetic cause of Hb disorders, and complex rearrangements and globin gene fusions can also occur. Thalassemias: Thalassemias are quantitative defects that lead to reduced levels of one type of globin chain, creating an imbalance in the ratio of alpha-like chains to beta-like chains. As noted above, this ratio is normally tightly regulated to prevent excess globin chains of one type from accumulating. The excess chains that fail to incorporate into Hb form non-functional aggregates that precipitate within the RBC. This can lead to premature RBC destruction in the bone marrow (beta thalassemia) and/or in the peripheral blood (alpha thalassemia). Types:
Alpha
Beta (Major)
Beta (Minor)

Hemoglobin variants
Haemoglobin variant are not necessarily pathological. For example, haemoglobin Valletta and haemoglobin Marseille are two haemoglobin variants which are non-pathological

HbS
HbC
HbE
Hb Barts
Hb D-Punjab
HbO (Hb O-Arab)
Hb G-Philadelphia
Hb H
Hb Constant Spring
Hb Hasharon
Hemoglobin Kenya
Hb Korle-Bu
Hb Lepore
Hb M
Hb Kansas
Hb J
Hb N-Baltimore
Hb Hope
Hb Pisa

Electrophoretic migration patterns
Hemoglobin variants can be detected by gel electrophoresis.
Cephalopelvic disproportion exists when the capacity of the pelvis is inadequate to allow the fetus to negotiate the birth canal. This may be due to a small pelvis, a nongynecoid pelvic formation, a large fetus, an unfavorable orientation of the fetus, or a combination of these factors. Certain medical conditions may distort pelvic bones, such as rickets or a pelvic fracture, and lead to CPD. Transverse diagonal measurement has been proposed as a predictive method. Causes
A large fetus can be one cause of CPD. A large fetus can be caused by gestational diabetes, postterm pregnancy, genetic factors, and multiparity. The shape of the pelvis can also be a cause of CPD. The pelvis may be too small, or the shape of the pelvis may be malformed. Shorter women are more likely to have CPD as are adolescents. Diagnosis
Diagnosis of CPD may be made when there is failure to progress, but not all cases of prolonged labour are the result of CPD. Use of ultrasound to measure the size of the fetus in the womb is controversial, as these methods are often inaccurate and may lead to unnecessary caesarian section; a trial of labour is often recommended even if size of the fetus is estimated to be large.Theoretically, pelvimetry may identify cephalo-pelvic disproportion. However, a womans pelvis loosens up before birth (with the help of hormones). A Cochrane review in 2017 found that there was too little evidence to show whether pelvimetry is beneficial and safe when the baby is in cephalic presentation.